cmd/go: confusion with module-aware get changes

[anacrolix]

Previously go get would check out code necessary to install something. With go modules, that changes. go install is now required to install something external to the current module. Go get will merely check out and add dependencies (so far as I can tell).

While the new behavior seems superior, it is surprising. I couldn't find any clarification on this. I'm also not sure how one would prevent go install from downloading code.

[mvdan]

I'm also not sure how one would prevent go install from downloading code.

Maybe you want #26361. Or perhaps one of the existing -getmode modes.

I couldn't find any clarification on this.

I think you want go help module-get. From the last paragraph in go help get:

This text describes the behavior of get when using GOPATH
to manage source code and dependencies.
If instead the go command is running in module-aware mode,
the details of get's flags and effects change, as does 'go help get'.
See 'go help modules' and 'go help module-get'.

[mvdan]

Milestoned for 1.11 in case there's anything else to do here. cc @rsc @bcmills

[bcmills]

I'm also not sure how one would prevent go install from downloading code.

From downloading code for existing dependencies, or from adding new dependencies?
(Adding new dependencies is #26361.)

[anacrolix]

If I want to install an arbitrary command, like go get used to do, what do I do now? If I want to install an arbitrary command, without downloading anything (what go install used to do), what now?

[earthboundkid]

I find the new behavior confusing as well.

$ mkdir /tmp/gopath
$ GO111MODULE=on GOPATH=/tmp/gopath go1.11beta2 get -v github.com/baltimore-sun-data/boreas
go: cannot find main module root; see 'go help modules'
$ GO111MODULE=on GOPATH=/tmp/gopath go1.11beta2 install -v github.com/baltimore-sun-data/boreas
go: cannot find main module root; see 'go help modules'

Is there a way to install arbitrary CLI tools with the go command any more, or do I have to git clone instead?

[myitcv]

@carlmjohnson yes you can use go install, but you will need a go.mod file, i.e. a module, as the starting point for that.

So if you want these tools to be generally available you could do something like:

mkdir -p $HOME/gotools
cd $HOME/gotools
mkdir bin
export GOBIN=$HOME/gotools/bin
go mod init gotools

GOBIN is a way of specifying exactly where programs should be installed.

Then:

go install github.com/baltimore-sun-data/boreas

Notice how you don't care what value is set for GOPATH; GOBIN becomes the relevant directory.

You might then also want to add the export above to your .bashrc or equivalent.

[earthboundkid]

Doesn't work:

$ GO111MODULE=on go1.11beta2 mod init whatever
go: cannot find main module root; see 'go help modules'

[bcmills]

Is there a way to install arbitrary CLI tools with the go command any more, or do I have to git clone instead?

That's #24250.

[bcmills]

@carlmjohnson, mod -init was changed to mod init after go1.11beta2. Either build from head or use the older spelling of the flag.

[earthboundkid]

$ GO111MODULE=on GOPATH=/tmp/gopath go1.11beta2 mod -init
go: cannot determine module path for source directory /tmp/gopath (outside GOPATH, no import comments)
$ GO111MODULE=on GOPATH=/tmp/gopath go1.11beta2 mod -init whatever
go mod: mod takes no arguments

My Go projects (including Boreas) all include these installation instructions in the README:

First install Go. If you just want to install the binary to your current directory and don't care about the source code, run GOBIN="$(pwd)" GOPATH="$(mktemp -d)" go get github.com/baltimore-sun-data/boreas.

It looks like for Go 1.12, if #24250 doesn't happen, I will need to change the instructions to

git clone $REPO
cd $PKG
GOBIN=$(pwd)/../bin GOPATH=$(mktemp -d) go install -v ./...

Three lines instead of one is not the end of the world, but it would be nice if I could just say to run a single command.

[myitcv]

I think (per #26591 (comment)) this is covered by #24250; please shout if that's not the correct conclusion.