Reconsider default of go.installDependenciesWhenBuilding

[segevfiner]

Do any Go tools we use still depend on installed packages, that is go build -i? If the answer is no, then as AFAIK installing dependencies is just a waste of time and space at that point and we should consider changing the default of go.installDependenciesWhenBuilding to false.

I think it's a mechanism left for backwards compatibility for stuff that depended on it, from the Go 1.10 release notes:

Installing dependency packages should not be necessary in general, and the very concept of installed packages may disappear in a future release.

— https://golang.org/doc/go1.10#build

[ramya-rao-a]

I am not an expert on the go build command and would like to loop in a few more people into this discussion.

Looping in @mattetti who made the initial PR #718 to add the -i flag to the go build command
Looping in @ardan-bkennedy who I know via #1064 uses the -i flag
Looping in @stamblerre who I hope can loop in someone working on the go command itself

[mattetti]

The old advice to add the -i flag for speed, as in go build -i or go test -i, is no longer necessary: builds run just as fast without -i. For more details, see go help cache.

It's quite clear that this flag isn't needed and might indeed slow things down. Thanks @segevfiner

[stamblerre]

/cc @jayconrod as the go command expert, but it sounds to me like building without -i sounds like the correct approach, particularly now that we have modules

[jayconrod]

Assuming nothing actually depends on .a files being installed into $GOPATH/pkg, I don't think this flag is necessary anymore.

In GOPATH mode, there may be some performance cost to using -i, since it will be copying .a files out of the cache into $GOPATH/pkg.

In module mode, I don't think -i has any effect, since we don't install .a files.

[ramya-rao-a]

So, we are leaning towards not using -i regardless of whether one is using modules or not, correct?

[segevfiner]

Seems like it...? I think the only thing we need to make sure is that we don't use some tool that otherwise depends on $GOPATH/pkg and didn't learn to rely on the Go build cache instead.

[segevfiner]

Looks like github.com/mdempsky/gocode (non-modules) still relies on "go/pkg" installed packages as it doesn't show any completion for me when I disable go.installDependenciesWhenBuilding.

[ramya-rao-a]

Thanks @segevfiner

People not using modules or the language server still end up using github.com/mdempsky/gocode, so we will keep this default value as is for now.