cmd/go: build fails when using GIT_DIR environment variable

[horacimacias]

What version of Go are you using (go version)?

$ go version
go version go1.19.1 darwin/arm64

Does this issue reproduce with the latest release?

yes

What operating system and processor architecture are you using (go env)?

go env Output

$ go env
GO111MODULE=""
GOARCH="arm64"
GOBIN=""
GOCACHE="/Users/...../Library/Caches/go-build"
GOENV="/Users/...../Library/Application Support/go/env"
GOEXE=""
GOEXPERIMENT=""
GOFLAGS=""
GOHOSTARCH="arm64"
GOHOSTOS="darwin"
GOINSECURE=""
GOMODCACHE="/Users/...../go/pkg/mod"
GOOS="darwin"
GOPATH="/Users/..../go"
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/opt/homebrew/Cellar/go/1.19.1/libexec"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/opt/homebrew/Cellar/go/1.19.1/libexec/pkg/tool/darwin_arm64"
GOVCS=""
GOVERSION="go1.19.1"
GCCGO="gccgo"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="..../go.mod"
GOWORK=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -arch arm64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/0y/6l073n8s6gj4gzqccdtb009h3rtc0w/T/go-build757008333=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

Create a project with the .git folder being renamed as testgit instead of the default .git.
All git operations function normally as long as GIT_DIR=testgit is passed through the environment.
Try to build the project using

env GIT_DIR=testgit go build ./...

What did you expect to see?

Success building project

What did you see instead?

error obtaining VCS status: exit status 128
	Use -buildvcs=false to disable VCS stamping.

Looks like go build is not considering that the git directory may have been overriden using GIT_DIR.
If I rename my testgit folder to the default .git and do not use GIT_DIR environment variable, go build ./... succeeds.

[seankhliao]

cc @bcmills @matloob

[bcmills]

@horacimacias, what was the complete stderr output of the failing go build command?

[horacimacias]

running env GIT_DIR=testgit go build ./... gave me

error obtaining VCS status: exit status 128
	Use -buildvcs=false to disable VCS stamping.

[bcmills]

So, probably a good starting point would be to fix cmd/go/internal/vcs.gitStatus to include the command's stderr output as part of the error so that this can be diagnosed further.

[horacimacias]

adding -v gave a bit more information:

env GIT_DIR=testgit go build -v ./...

# cd /Users/some_other_folder; git status --porcelain
fatal: not a git repository: 'testgit'
error obtaining VCS status: exit status 128
	Use -buildvcs=false to disable VCS stamping.

looks like that cd /Users/some_other_folder is go trying to "navigate up" until it finds a .git folder? it's assuming .git is the GIT_DIR which is the default, but it's not using the overriden value from env variable.

go/src/cmd/go/internal/vcs/vcs.go

Lines 245 to 248 in ebb71ad

	RootNames: []rootName{
	{filename: ".git", isDir: true},
	},

In case this is of any help, in my case I have a "root" project git the "normal" .git folder there.
Inside this project, I have some "sample go projects" where a testgit folder is used, to avoid using .git again since this is not the root of the overall project.
In this "sample go projects", I can perform git operations using GIT_DIR and everything is ok.
In fact I can also do env GIT_DIR=testgit git status --porcelain and I get no output or error.

Running env GIT_DIR=testgit git -c log.showsignature=false show -s --format=%H:%ct also succeeds:

1e55531ca86b3e8099149ff7aec173db95c777b0:1669015511

[horacimacias]

are there any tests on this feature I can have a look at? if somebody points me to some starting point I may be able to contribute with a PR

[bcmills]

@horacimacias, the existing tests for VCS stamping are in GOROOT/src/cmd/go/testdata/script/*buildvcs*.txt. (See the README in that directory for a description of the script language.)