cmd/go: print default GOBIN when running "go env GOBIN" if not set

[leitzler]

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

$ go version
go version go1.13 linux/amd64

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="amd64"
GOBIN=""
GOCACHE="/root/.cache/go-build"
GOENV="/root/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/local/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
AR="ar"
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-build575410569=/tmp/go-build -gno-record-gcc-switches"

What did you do?

Run go env GOBIN

What did you expect to see?

The current evaluated path to GOBIN.

It has bitten me a few times where I install tools with go install and then want to run them, without relying on having GOBIN in my path. I can't really see any reason why go env GOBIN shouldn't return the current one.

Also see @rsc comment in #23439 (comment)

What did you see instead?

An empty line.

[leitzler]

@gopherbot, please add label GoCommand

[mvdan]

There's also go list -f {{.Target}} path/to/main, but that requires knowing the full package path (and resolving it!), and doesn't return the directory. The directory can be useful for many things, such as adding it to PATH in some environments.

[mvdan]

Also note that some env vars like go env GOPATH and go env GOCACHE correctly return the default values when the user hasn't set one up. I'm not sure if there are any other flags that are inconsistent like GOBIN; after a quick scan I could only find GOTMPDIR, which might not have a static default value.

[bcmills]

go env GOBIN does return the value of GOBIN:

~$ GOBIN=/tmp/foo go env GOBIN
/tmp/foo

GOPATH[0]/bin is used very similarly in module mode, but it is not yet the same — especially in GOPATH mode, which despiteallobjections continues to exist.

[bcmills]

Duplicate of #23439