Using forked package import in Go

Suppose you have a repository at github.com/someone/repo and you fork it to github.com/you/repo. You want to use your fork instead of the main repo, so you do a

go get github.com/you/repo

Now all the import paths in this repo will be "broken", meaning, if there are multiple packages in the repository that reference each other via absolute URLs, they will reference the source, not the fork.

Is there a better way as cloning it manually into the right path?

git clone git@github.com:you/repo.git $GOPATH/src/github.com/someone/repo

If you are using go modules. You could use replace directive

> The replace directive allows you to supply another import path that might
> be another module located in VCS (GitHub or elsewhere), or on your
> local filesystem with a relative or absolute file path. The new import
> path from the replace directive is used without needing to update the
> import paths in the actual source code.

So you could do below in your go.mod file

module some-project

go 1.12

require (
	github.com/someone/repo v1.20.0
)

replace github.com/someone/repo => github.com/you/repo v3.2.1

where v3.2.1 is tag on your repo. Also can be done through CLI

go mod edit -replace="github.com/someone/repo@v0.0.0=github.com/you/repo@v1.1.1"

To handle pull requests

• fork a repository github.com/someone/repo to github.com/you/repo
• download original code: go get github.com/someone/repo
• be there: cd "$(go env GOPATH)/src"/github.com/someone/repo
• enable uploading to your fork: git remote add myfork https://github.com/you/repo.git
• upload your changes to your repo: git push myfork

http://blog.campoy.cat/2014/03/github-and-go-forking-pull-requests-and.html

To use a package in your project

https://github.com/golang/go/wiki/PackageManagementTools

One way to solve it is that suggested by Ivan Rave and http://blog.campoy.cat/2014/03/github-and-go-forking-pull-requests-and.html -- the way of forking.

Another one is to workaround the golang behavior. When you go get, golang lays out your directories under same name as in the repository URI, and this is where the trouble begins.

If, instead, you issue your own git clone, you can clone your repository onto your filesystem on a path named after the original repository.

Assuming original repository is in github.com/awsome-org/tool and you fork it onto github.com/awesome-you/tool, you can:

cd $GOPATH
mkdir -p {src,bin,pkg}
mkdir -p src/github.com/awesome-org/
cd src/github.com/awesome-org/
git clone git@github.com:awesome-you/tool.git # OR: git clone https://github.com/awesome-you/tool.git
cd tool/
go get ./...

golang is perfectly happy to continue with this repository and doesn't actually care some upper directory has the name awesome-org while the git remote is awesome-you. All import for awesome-org are resovled via the directory you have just created, which is your local working set.

In more length, please see my blog post: Forking Golang repositories on GitHub and managing the import path

edit: fixed directory path

If your fork is only temporary (ie you intend that it be merged) then just do your development in situ, eg in $GOPATH/src/launchpad.net/goamz.

You then use the features of the version control system (eg git remote) to make the upstream repository your repository rather than the original one.

It makes it harder for other people to use your repository with go get but much easier for it to be integrated upstream.

In fact I have a repository for goamz at lp:~nick-craig-wood/goamz/goamz which I develop for in exactly that way. Maybe the author will merge it one day!

Here's a way to that works for everyone:

Use github to fork to "my/repo" (just an example):

go get github.com/my/repo
cd ~/go/src/github.com/my/repo
git branch enhancement
rm -rf .
go get github.com/golang/tools/cmd/gomvpkg/…
gomvpkg <<oldrepo>> ~/go/src/github.com/my/repo
git commit

Repeat each time when you make the code better:

git commit
git checkout enhancement
git cherry-pick <<commit_id>>
git checkout master

Why? This lets you have your repo that any go get works with. It also lets you maintain & enhance a branch that's good for a pull request. It doesn't bloat git with "vendor", it preserves history, and build tools can make sense of it.

Instead of cloning to a specific location, you can clone wherever you want.
Then, you can run a command like this, to have Go refer to the local version:

go mod edit -replace github.com/owner/repo=../repo

https://golang.org/cmd/go#hdr-Module_maintenance

The answer to this is that if you fork a repo with multiple packages you will need to rename all the relevant import paths. This is largely a good thing since you've forked all of those packages and the import paths should reflect this.

Use vendoring and submodules together

1. Fork the lib on github (go-mssqldb in this case)
2. Add a submodule which clones your fork into your vendor folder but has the path of the upstream repo
3. Update your import statements in your source code to point to the vendor folder, (not including the vendor/ prefix). E.g. vendor/bob/lib => import "bob/lib"

E.g.

cd ~/go/src/github.com/myproj

mygithubuser=timabell
upstreamgithubuser=denisenkom
librepo=go-mssqldb

git submodule add "git@github.com:$mygithubuser/$librepo" "vendor/$upstreamgithubuser/$librepo"

Why

This solves all the problems I've heard about and come across while trying to figure this out myself.

• Internal package refs in the lib now work because the path is unchanged from upstream
• A fresh checkout of your project works because the submodule system gets it from your fork at the right commit but in the upstream folder path
• You don't have to know to manually hack the paths or mess with the go tooling.

More info

• https://git-scm.com/book/en/v2/Git-Tools-Submodules

• https://stackoverflow.com/q/34973883/10245

• https://github.com/denisenkom/go-mssqldb/issues/406

• https://github.com/golang/go/wiki/PackageManagementTools#go15vendorexperiment

The modern answer (go 1.15 and higher, at least).

go mod init github.com/theirs/repo

Make an explicit init arg that is the ORIGINAL package names. If you don't include the repo name, it will assume the one in gopath. But when you use go modules, they no longer care where they are on disk, or where git actually pulls dependencies from.

To automate this process, I wrote a small script. You can find more details on my blog to add a command like "gofork" to your bash.

function gofork() {
  if [ $# -ne 2 ] || [ -z "$1" ] || [ -z "$2" ]; then
    echo 'Usage: gofork yourFork originalModule'
    echo 'Example: gofork github.com/YourName/go-contrib github.com/heirko/go-contrib'
    return
  fi
   echo "Go get fork $1 and replace $2 in GOPATH: $GOPATH"
   go get $1
   go get $2
   currentDir=$PWD
   cd $GOPATH/src/$1
   remote1=$(git config --get remote.origin.url)
   cd $GOPATH/src/$2
   remote2=$(git config --get remote.origin.url)
   cd $currentDir
   rm -rf $GOPATH/src/$2
   mv $GOPATH/src/$1 $GOPATH/src/$2
   cd $GOPATH/src/$2
   git remote add their $remote2
   echo Now in $GOPATH/src/$2 origin remote is $remote1
   echo And in $GOPATH/src/$2 their remote is $remote2
   cd $currentDir
}
 
export -f gofork

You can use command go get -f to get you a forked repo

in your Gopkg.toml file add these block below

[[constraint]]
  name = "github.com/globalsign/mgo"
  branch = "master"
  source = "github.com/myfork/project2"

So it will use the forked project2 in place of github.com/globalsign/mgo