How Go caches downloaded packages

Here I intend to summarize how the Go package cache system works, after spending half of my afternoon running tests and figuring out this weird thing.

First off, to create a new Go project outside the awful GOPATH directory, you run:

mkdir my-project
cd my-project
go mod init my-project

This will create a go.mod file.

To add a dependency from GitHub, you run:

go get github.com/username/reponame

This will create a go.sum file, which contains the dependency tree. The package files themselves will be downloaded and buried within ~/go/pkg/mod directory, so they are effectively cached at global, machine-wide scope.

To list the packages inside my-project, run:

go list ./...

This won’t list globally downloaded, cached dependencies installed with go get.

To list the packages installed (not the cached ones) globally, run:

go list ...

Downloaded dependencies will be listed if you are in my-project folder, and if they have been downloaded already. If you run the command above from within a project directory, it will download and install any missing packages for current project, and then they will be listed.

So, if you’re outside my-project directory, there’s no way to list globally cached packages.

There’s no way to remove a globally cached package from cache individually. All you can do is delete the whole cache, with:

go clean -cache -modcache -i -r