I've been setting GOBIN manually for a while now. I also run go install cmd/go somewhat regularly, to test changes I make to the tool.

Recently, I started noticing a $GOBIN/go binary, which makes no sense to me. I always thought that go install cmd would populate $GOROOT/bin, not $GOBIN. The recent changes in 530097f seem to agree with me:

Note that the Go distribution's executables are installed in $GOROOT/bin (for executables invoked by people) or $GOTOOLDIR (for executables invoked by the go command;
defaults to $GOROOT/pkg/$GOOS_GOARCH) instead of $GOBIN.

Below is how I reproduced this on my system, which is running a somewhat recent master version. I verified that this regression doesn't show in 1.12.6 by building that tag from source and testing again.

$ go version
go version devel +7a4d02387f Sun Jun 16 20:04:54 2019 +0000 linux/amd64
$ go env
GO111MODULE="on"
GOARCH="amd64"
GOBIN="/home/mvdan/go/bin"
GOCACHE="/home/mvdan/go/cache"
GOENV="/home/mvdan/.config/go/env"
GOEXE=""
GOFLAGS="-ldflags=-w"
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GONOPROXY="brank.as/*"
GONOSUMDB="brank.as/*"
GOOS="linux"
GOPATH="/home/mvdan/go"
GOPRIVATE="brank.as/*"
GOPROXY="https://proxy.golang.org"
GOROOT="/home/mvdan/tip"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/home/mvdan/tip/pkg/tool/linux_amd64"
GCCGO="gccgo"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD="/dev/null"
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-build811082871=/tmp/go-build -gno-record-gcc-switches"
$ echo $GOBIN
/home/mvdan/go/bin
$ which go
/home/mvdan/tip/bin/go
$ ls ~/go/bin/go
ls: cannot access '/home/mvdan/go/bin/go': No such file or directory
$ go install cmd/go
$ ls ~/go/bin/go
/home/mvdan/go/bin/go*

I don't have the time to bisect now, but I can do that later this week if that's necessary. One perhaps important piece of information is that this problem disappears if I stop exporting $GOBIN; perhaps the bug is that go install isn't properly ignoring an explicitly set $GOBIN when installing cmd.

The fact that make.bash unsets the variable seems to back up this theory. However, that's #14340, which seems related but not the same issue.

/cc @bcmills @jayconrod