If a plugin supports downloading & compiling from source, you can specify `ref:foo` where `foo` is a specific branch, tag, or commit. You'll need to use the same name and reference when uninstalling too.
When asdf installs a package it creates shims for every executable program in that package in a `$ASDF_DATA_DIR/shims` directory (default `~/.asdf/shims`). This directory being on the `$PATH` (by means of `asdf.sh` or `asdf.fish`) is how the installed programs are made available in the environment.
The shims themselves are really simple wrappers that `exec` a helper program `asdf exec` passing it the name of the plugin and path to the executable in the installed package that the shim is wrapping.
The `asdf exec` helper determines the version of the package to use (as specified in `.tool-versions` file, selected by `asdf local ...` or `asdf global ...`), the final path to the executable in the package installation directory (this can be manipulated by the `exec-path` callback in the plugin) and the environment to execute in (also provided by the plugin - `exec-env` script), and finally it executes it.
Because this system uses `exec` calls, any scripts in the package that are meant to be sourced by the shell instead of executed need to be accessed directly instead of via the shim wrapper. The two `asdf` commands: `which` and `where` can help with this by returning the path to the installed package:
If for some reason you want to by-pass asdf shims or want your environment variables automatically set upon entering your project's directory, the [asdf-direnv](https://github.com/asdf-community/asdf-direnv) plugin can be helpful. Be sure to check its README for more details.
