Golang: How to use vgo? error: "cannot find package"

Question

I have a project which is currently under my GOPATH /usr/local/go/src/
Then I went inside my project root and ran: go get -u golang.org/x/vgo
In my main.go I want to use lib httprouter so I added in import statement:

import ( "github.com/julienschmidt/httprouter" )
I ran vgo build
Then when I start to run my server as usual I get the following error:

main.go:8:2: cannot find package "github.com/julienschmidt/httprouter" in any of: /usr/local/go/src/github.com/julienschmidt/httprouter (from $GOROOT) /Users/myuser/go/src/github.com/julienschmidt/httprouter (from $GOPATH)

I understand the error, it seems to be searching for httprouter under GOPATH or GOROOT. So do I have to do anything else to just let vgo do its thing and I can run my server successfully?

Before doing `vgo build` like in normal `go` you need to ran `vgo get` in your project directory — ttomalak, Jun 11 '18 at 19:38
Did you create an empty `go.mod` file before running `vgo build`? Did `vgo build` generate the contents of `go.mod`? Does `go.mod` contain `httprouter`? When you say "start to run my server," what command did you run? — Tyler B, Jun 12 '18 at 13:42

Tyler B · Answer 1 · 2018-06-26T13:55:57.093

Using `vgo build`

Here is a "Hello, World" walk-through of using vgo, including common errors and how to respond to them.

$ go get -u golang.org/x/vgo
$ cd /tmp/hello # Outside of GOPATH.

$ cat main.go

package main

import "fmt"

func main() {
    fmt.Println("Hello, World")
}

$ vgo build

cannot determine module root; please create a go.mod file there

This error tells us we need to specify what the root of our vgo module is. A module is a collection of packages (possibly one) versioned together. Create an empty go.mod file to signify this is the module root:
```
$ touch go.mod
```

Try building again: $ vgo build.

vgo: cannot determine module path for source directory
/tmp/hello (outside GOPATH, no import comments)

This error tells us vgo doesn't know the import path of our package. There are two ways to tell it:
1. Add a module statement to go.mod.
2. Add an import comment to our package.
We'll go with option 2 right now and come back to option 1. Change the first line of main.go to be:
```
package main // import "my/import/path/hello"
```
$ vgo build one last time.
Run the binary: $ ./hello
```
Hello, World
```

Note: go.mod now contains a module line (option 1 above):

$ cat go.mod 
module my/import/path/hello

If you are inside your GOPATH, the error in step 5 should not occur - vgo build should automatically figure out you're inside your GOPATH and add the module line accordingly.

Using `vgo run` (without using `vgo build`)

For this example, lets use the hello.go from the A Tour of Versioned Go (vgo):

$ go get -u golang.org/x/vgo
$ mkdir /tmp/hello2
$ curl -sS https://swtch.com/hello.go >hello.go

$ vgo run hello.go

cannot determine module root; please create a go.mod file there

$ touch go.mod

$ vgo run hello.go

vgo: resolving import "rsc.io/quote"
vgo: finding rsc.io/quote (latest)
vgo: adding rsc.io/quote v1.5.2
Hello, world.

thanks for answer. I wonder can you include parallel step of run but without binary, I normally do go run main.go, when developing I also use some autoreloaded, `gin` what would be the equivalent of go run main.go with vgo? — CommonSenseCode, Jun 12 '18 at 14:27
You can run `vgo run` directly. :) I updated the answer with an example. — Tyler B, Jun 13 '18 at 16:06

Golang: How to use vgo? error: "cannot find package"

1 Answers1

Using vgo build

Using vgo run (without using vgo build)

Using `vgo build`

Using `vgo run` (without using `vgo build`)