How to reliably get the projects root in go?

For now I used runtime.Caller(0) in combination with path.Dir and filepath.Abs to get the path to the currently executed file and get the project root relative to it.

So lets say I've a folder structure like this:

$GOPATH/src/example.org/myproject
$GOPATH/src/example.org/myproject/main.go
$GOPATH/src/example.org/myproject/path
$GOPATH/src/example.org/myproject/path/loader.go

If I want my project root I call the loader.go which in turn gets its path with runtime.Caller(0) and then goes up one folder to reach the project root.

The problem is when using go test -cover the executed file is not in its normal place anymore but in a special sub directory for the testing and coverage analysis.
runtime.Caller(0) gives me the following:

example.org/myproject/path/_test/_obj_/loader.go

Running it through path.Dir and filepath.Abs will give me:

$GOPATH/src/example.org/myproject/path/example.org/myproject/path/_test/_obj_

When I go up from there I won't reach the project root but something totally different obviously. So my questions stands:
Is there any reliable way of getting the project root?

You can build it from the $GOPATH env variable:

gp := os.Getenv("GOPATH")
ap := path.Join(gp, "src/example.org/myproject")
fmt.Println(ap)

That will yield the absolute path to your paroject dir:

/path/to/gopath/src/example.org/myproject

This obviously only works when GOPATH is set. aka. on your dev machine. On production you need to supply directories via a config file.

See this answer. In case you are using go ~ 1.8, func Executable() (string, error) is an option I stumbled over when I needed it. I tested briefly how it interacts with go test -cover and it seems to work fine:

> func Executable() (string, error)
>
> Executable returns the path name for the executable that started the current process. There is no guarantee that the path is still pointing to the correct executable. If a symlink was used to start the process, depending on the operating system, the result might be the symlink or the path it pointed to. If a stable result is needed, path/filepath.EvalSymlinks might help.

package main

import (
    "fmt"
    "os"
    "path"
)

func main() {
    e, err := os.Executable()
    if err != nil {
        panic(err)
    }
    path := path.Dir(e)
    fmt.Println(path)
}

The test:

binpath.go:

package binpath

import (
    "os"
    "path"
)

func getBinPath() string {
    e, err := os.Executable()
    if err != nil {
        panic(err)
    }
    path := path.Dir(e)
    return path
}

binpath_test.go:

package binpath

import (
    "fmt"
    "testing"
)

func TestGetBinPath(t *testing.T) {
    fmt.Println(getBinPath())
}

Results in something like /tmp/go-build465775039/github.com/tworabbits/binpath/_test

Abs returns an absolute representation of path. If the path is not absolute it will be joined with the current working directory to turn it into an absolute path

absPath, err := filepath.Abs()
if err != nil {
	panic("Ooops)
}