use last gopath element when installing tools

[jrwren]

#1966

[AlexRouSg]

Why use last? The go get behavior is to use the first.

[jrwren]

Why use last? The go get behavior is to use the first.

I thought so too, but that is not what I observed. Can you double check that you observe it installing to first?

[AlexRouSg]

Yes, that is how I observe it to work on Linux and Windows. This is even documented behavior.

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

When checking out a new package, get creates the target directory GOPATH/src/. If the GOPATH contains multiple entries, get uses the first one. For more details see: 'go help gopath'.

[jrwren]

That is pretty definite documentation. I wonder why I think I observed what I observed. I'll change this.

I also had a question re: calling go install? Why use -o rather than calling go install with GOPATH set?

[AlexRouSg]

I find that weird too. go install will install to the same gopath that the package is in. And if you're changing gopath to be a single path then that shouldn't even cause problems even if you have the same package in multiple gopaths.

[jrwren]

I realize now that the same code paths in vscode-go are made to install the tools even when there is no GOPATH, e.g. the GOPATH is infered per project or the go project uses go modules. I'm going to change the index to 0 and hopefully that is acceptable.

[ramya-rao-a]

I also had a question re: calling go install? Why use -o rather than calling go install with GOPATH set?

To support Go modules, we use forks of gocode and godef. But we do not want these forks to replace the original binaries. This is because the forks are slower than the originals, and we dont want to use the forks when you are not using Go modules.

In order to do this, we use go get -d so that the tool is not installed and then use go build -o so that we are free to rename the binary as gocode-gomod/godef-gomod.

[ramya-rao-a]

Thanks for the PR @jrwren

Multiple gopath was not an issue previously when installing tools, as we didnt use it directly for anything. It was only set as an environment variable.

Now that we use it directly to build the forks of gocode and godef, this fix is necessary