Automatically define GOPATH on a per project basis

(Q2 2018:
Note that with the vgo (now “module”) project, GOPATH might end up being deprecated in favor of a project-based workflow. That would avoid the manual project-based GOPATH I was proposing below, two years ago)

With Go 1.11 (August 2018), GOPATH can be optional, with modules.

You have a similar idea expressed in Manage multiple GOPATH dirs with ease, by Herbert Fischer (hgfischer), for a Linux/Unix environment (base on the question already mention in the comments above):

Just include the following snippet in your ~/.bashrc (or ~/.bash_profile) and reload your shell environment with source ~/.bashrc.
This snippet will create a shell function that will override the builtin command cd with a customized one that scans the entered directory, and every other above, for a file named .gopath.

cd () {
    builtin cd "$@"
    cdir=$PWD
    while [ "$cdir" != "https://stackoverflow.com/" ]; do
        if [ -e "$cdir/.gopath" ]; then
            export GOPATH=$cdir
            break
        fi
        cdir=$(dirname "$cdir")
    done
}

Now you just need to create a .gopath file in every directory you want as your GOPATH and every time you enter this directory, the redefined cd function will set the GOPATH of your current environment to this directory.

Update 2017: if you don’t want to modify your environment, you can still use one GOPATH per project, by opening the src folder of that project in Visual Studio Code (vscode, which is a multi-platform IDE), combined with the extension “Go for Visual Studio Code”.

In that IDE, you can:

• keep your global unique GOPATH in a setting called go.toolsGopath.
• infer your current GOPATH with a setting called go.inferGopath

That way, VSCode will install a collection of tools in your global GOPATH (for you to use outside VSCode as well).
See “Go tools that the Go extension depends on”: godep, golint, guru, godoc, …

And yet, your GOPATH for your project will be the parent folder of src:

That works when you compile/install your project from the IDE.
If you want to do it from the command line, the original answer above would still apply.