cmd/go: pollutes environment variables on Plan 9

[fhs]

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

$ go version
go version devel +master Wed Oct 16 20:56:59 EDT 2019 plan9/386

What operating system and processor architecture are you using (go env)?

go env Output

$ go env
GO111MODULE='on'
GOARCH='386'
GOBIN=''
GOCACHE='/usr/fhs/lib/cache/go-build'
GOENV='/usr/fhs/lib/go/env'
GOEXE=''
GOFLAGS=''
GOHOSTARCH='386'
GOHOSTOS='plan9'
GONOPROXY=''
GONOSUMDB=''
GOOS='plan9'
GOPATH='/home/fhs/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/home/big/go'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLDIR='/home/big/go/pkg/tool/plan9_386'
GCCGO='gccgo'
GO386='sse2'
AR='ar'
CC='6c'
CXX='g++'
CGO_ENABLED='0'
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 -m32 -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build631500855=/tmp/go-build -gno-record-gcc-switches'

What did you do?

cpu% cd $GOROOT/src/cmd/go
cpu% ls /env > /tmp/1
cpu% go test -c
cpu% ls /env > /tmp/2
cpu% diff -c /tmp/1 /tmp/2
/tmp/1:1,8 - /tmp/2:1,26
  '/env/*'
  /env/0
+ /env/AR
+ /env/CC
+ /env/CGO_ENABLED
+ /env/CXX
+ /env/GCCGO
+ /env/GIT_SSH_COMMAND
+ /env/GIT_TERMINAL_PROMPT
  /env/GO111MODULE
+ /env/GO386
+ /env/GOARCH
+ /env/GOCACHE
+ /env/GOENV
+ /env/GOHOSTARCH
+ /env/GOHOSTOS
+ /env/GOOS
  /env/GOPATH
+ /env/GOPROXY
+ /env/GOROOT
  /env/GOROOT_BOOTSTRAP
+ /env/GOSUMDB
+ /env/GOTOOLDIR
  /env/NPROC
  /env/apid
  /env/bootargs
cpu% ./go.test -test.run TestLocalImportsEasySub  # any test will do
PASS
cpu% ls /env > /tmp/3
cpu% diff -c /tmp/2 /tmp/3
/tmp/2:2,7 - /tmp/3:2,8
  /env/0
  /env/AR
  /env/CC
+ /env/CCACHE_DISABLE
  /env/CGO_ENABLED
  /env/CXX
  /env/GCCGO
/tmp/2:15,27 - /tmp/3:16,29
  /env/GOHOSTARCH
  /env/GOHOSTOS
  /env/GOOS
- /env/GOPATH
  /env/GOPROXY
  /env/GOROOT
  /env/GOROOT_BOOTSTRAP
  /env/GOSUMDB
  /env/GOTOOLDIR
+ /env/HOME
  /env/NPROC
+ /env/TMPDIR
  /env/apid
  /env/bootargs
  /env/bootdisk
cpu% go version
go: creating work dir: stat /tmp/cmd-go-test-744136408: '/tmp/cmd-go-test-744136408' file does not exist
cpu% cat /env/TMPDIR; echo
/tmp/cmd-go-test-744136408
cpu% 

What did you expect to see?

Working go command after testing cmd/go.

What did you see instead?

Environment polluted with $TMPDIR, which breaks cmd/go.

This is likely related to issue #25234.

@gopherbot please add labels OS-Plan9, NeedsFix

[bcmills]

The change here almost certainly belongs in the os package, not a special case in cmd/go.

[bcmills]

Duplicate of #25234

[gopherbot]

Change https://golang.org/cl/202088 mentions this issue: runtime, os: don't share environment variables between processes on Plan 9

[gopherbot]

Change https://golang.org/cl/236520 mentions this issue: runtime, syscall: use local cache for Setenv/Getenv in Plan 9