Go: cmd/go: run gives conflicting advice when using path@version syntax

[davecheney]

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

% go version
go version devel +97d5cb24b1 Sat Dec 22 09:37:04 2018 +0000 linux/amd64

Does this issue reproduce with the latest release?

unknown

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

go env Output

% go env

GOARCH="amd64"

GOBIN=""

GOCACHE="/home/dfc/.cache/go-build"

GOEXE=""

GOFLAGS=""

GOHOSTARCH="amd64"

GOHOSTOS="linux"

GOOS="linux"

GOPATH=""

GOPROXY=""

GORACE=""

GOROOT="/home/dfc/go"

GOTMPDIR=""

GOTOOLDIR="/home/dfc/go/pkg/tool/linux_amd64"

GCCGO="gccgo"

CC="gcc"

CXX="g++"

CGO_ENABLED="1"

GOMOD=""

CGO_CFLAGS="-g -O2"

CGO_CPPFLAGS=""

CGO_CXXFLAGS="-g -O2"

CGO_FFLAGS="-g -O2"

CGO_LDFLAGS="-g -O2"

PKG_CONFIG="pkg-config"

GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build125128327=/tmp/go-build -gno-record-gcc-switches"

What did you do?

Go 1.12beta1 (tip) does not permit @version syntax unless modules explicitly enabled, even if GOPATH is unset

% unset GOPATH && go run -v github.com/davecheney/[email protected]
package github.com/davecheney/[email protected]: cannot use path@version syntax in GOPATH mode

What did you expect to see?

env GO111MODULE=on go run -v github.com/davecheney/[email protected]

would download and build httpstat v1.0.0

What did you see instead?

% unset GOPATH && env GO111MODULE=on go run -v github.com/davecheney/[email protected]
missing $GOPATH

Running without modules enabled tells me I must enable modules even thought I don't have GOPATH set. Running _with_ modules enable tells me I must set GOPATH.

lucky(/tmp) % env GO111MODULE=on GOPATH=/tmp/ go run -v github.com/davecheney/[email protected]
package github.com/davecheney/[email protected]: can only use path@version syntax with 'go get'

Setting both tells me that this isn't supported.

a. Can go run path@version be supported? If not, why not?
b. Can the error messages be improved make it clearer sooner that the operation will not succeed once the correct permutation of environment variables is discovered.

[odeke-em]

Thank you for this report @davecheney!

Kindly paging @bcmills @rsc.

[jadekler]

Seems to not be working for me, either:

$ cd /tmp/whatever && unset GOPATH && go get cloud.google.com/[email protected]
go: cannot use path@version syntax in GOPATH mode

[ahmetb]

Hit this as well in #29575. Closing that as duplicate.

[rsc]

Only go get and module-manipulation commands take path@version.
go build, go run, etc do not.

[jadekler]

Go get does not take path@version for me. I've filed https://github.com/golang/go/issues/29659, since that appears to be different from the go run case that this issue was describing. (happy to dedupe if you prefer the conversation to happen here)

[ahmetb]

Can someone take a look at this please?

Example from https://golang.org/cmd/go/#hdr-Module_aware_go_get which is go get golang.org/x/[email protected] doesn't work and fails with the same error when GOPATH environment variable is not set.

This is breaking go-get’s ability as a package manager as the support for the go get -v github.com/rakyll/[email protected] syntax is currently not working.

[bcmills]

@ahmetb, this issue is about the diagnostic messages. If go get is not actually behaving as documented, please file that as a separate issue.

That said, from the detail in #29575 it appears that you are, in fact, running in GOPATH mode.
Per https://golang.org/cmd/go/#hdr-Preliminary_module_support:

If GO111MODULE=auto or is unset, then the go command enables or disables module support based on the current directory. Module support is enabled only when the current directory is outside GOPATH/src and itself contains a go.mod file or is below a directory containing a go.mod file.

[ahmetb]

@bcmills I'm still seeing this despite I'm not running in GOPATH mode. go get or go build uses modules just fine when I don't specify a @version syntax.

Here's a minimal repro with go1.12

dir=$(mktemp -d)

cd $dir

# write a go.mod to indicate go111module=on
echo 'module foo' > go.mod

go get module syntax uses go.mod file:

# unset all env vars, with the exception of $HOME (mock it) and $PATH (inherit it)

env -i HOME="$PWD/mock-home" PATH="$PATH" go build -o ./httpstat github.com/davecheney/httpstat

    go: finding github.com/davecheney/httpstat v1.0.0
    go: downloading github.com/davecheney/httpstat v1.0.0
    go: extracting github.com/davecheney/httpstat v1.0.0
    ...
    (works)

go get [email protected] syntax is not working in the same setup:

env -i HOME="$PWD/mock-home" PATH="$PATH" go build -o ./httpstat github.com/davecheney/[email protected]

can't load package: package github.com/davecheney/[email protected]: can only use path@version syntax with 'go get'

Would you still suggest I'm in "GOPATH mode"?

[bcmills]

@ahmetb, this issue is about the go command giving conflicting advice.

The advice from the commands you posted above does not conflict: it correctly indicates that, in module mode (which you are clearly in), you “can only use path@version syntax with 'go get'”.

[probonopd]

With Go 1.13, also running into

imports github.com/diskfs/go-diskfs/filesystem@squashfs: cannot use path@version syntax in GOPATH mode

This is so annoying. Especially because it does not tell one what to do.

[smikulcik]

From what I can tell, you just have to be in a package that has a go.mod file. Then you can get a particular version.

[nivekastoreth]

Thanks to @smikulcik's comment go get is at least minimally functional.

As someone who doesn't program in go and only uses it to install utilities written in go, it's extremely frustrating spending an hour trying to figure out how to install a simple application only to find out I have to pretend to be working on a project in order to install a version of a utility that's needed.

[AgrPriyank]

From what I can tell, you just have to be in a package that has a go.mod file. Then you can get a particular version.

As I understand it, path@version should be used in Golang specifically for version maintenance. Hence @smikulcik comment to run the command in directory with go.mod file makes sense. Go will try to download the repository to your src folder from Github and will try to maintain the version in the mod file.

[13rac1]

$ docker run -it golang:1.15-alpine
/go # echo $GOPATH
/go
/go # go run -v github.com/user/project@test
package github.com/user/project@test: can only use path@version syntax with 'go get'
/go # go install github.com/user/project@test
package github.com/user/project@test: can only use path@version syntax with 'go get'
/go # go get -u github.com/user/project@test
go: cannot use path@version syntax in GOPATH mode
/go # unset GOPATH
/go # echo $GOPATH

/go # go get -u github.com/user/project@test
go: cannot use path@version syntax in GOPATH mode <- I unset it! Yes, I know what the docs say, but still.
/go # export GO111MODULE=on
/ # go get -u github.com/user/project@test
go: downloading github.com/user/project v1.0.0-date-sha <- Should be test branch @latest, but that's separate.

@nivekastoreth FWIW I've written Go for the last five years and this is frustrating for me too.

These error messages are not helpful. Users should not need search the Internet for this error message to install an app from a git repository in an expected way. What steps can we take to make this _just_ work and fix this user/developer experience? The answer is not "RTFM" Essays about Go mod version-specific pitfalls and workarounds shouldn't need exist. What can we do?