cmd/go: env -w can set (but not remove) an invalid GOOS and GOARCH value

[jsign]

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="/home/ignacio/.cache/go-build"
GOENV="/home/ignacio/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/home/ignacio/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-build527315638=/tmp/go-build -gno-record-gcc-switches"

What did you do?

Write config file regarding GOOS with a typo:
~ % go env -w GOOS=linuxx

What did you expect to see?

Some error indicating the value being incorrect.

What did you see instead?

Command ran successfully and written to config file, then doing go env will result in an error:

~ % go env
cmd/go: unsupported GOOS/GOARCH pair linuxx/amd64

Despite this mean setting an invalid GOOS value, it can't be fixed with -w again:

~ % go env -w GOOS=linux
cmd/go: unsupported GOOS/GOARCH pair linuxx/amd64

So basically I had to edit $GOENV file manually to get unstuck.

The error output is the result of calling MkEnv() in main.go which eventually detects the invalid value and exits. This means that any -w attempt to fix the invalid value won't be reached to make it.

An option can be to do the same control setting a valid value with -w to avoid being invalid.
A similar thing happens if an invalid value is set with export GOOS=linuxx, but that's somehow OK since external env GOOS set isn't in go command control.

Similarly, the same situation happens with an invalid env -w GOARCH.

If checking these situations in env -w makes sense, I can make a PR adding this validation in checkEnvWrite() which I think would the correct place: one extra case "GOOS", "GOARCH":.
Some tests can also be added to cover this.

[smasher164]

I think it makes sense to check for a valid GOOS/GOARCH before writing in the first place, so checkEnvWrite seems like the right way to do this. /cc @rsc @bcmills

[bcmills]

Certainly go env should be made consistent one way or the other: if it accepts a value without error, then subsequent invocations of go env should not reject that value.

CC @jayconrod

[jsign]

Pushing things a bit, proper checking in go env -w isn't enough. Doing go env -u could lead to an incorrect combination too, e.g (my machine):

$ go env GOOS GOARCH
linux
amd64
$ go env -w GOOS=nacl GOARCH=amd64p32
$ go env 
(... works as expected since nacl/amd64p32 is a valid combination ...)
$ go env -u GOOS
(... works, which isn't correct)
$ go env 
cmd/go: unsupported GOOS/GOARCH pair linux/amd64p32

Basically, the go env -u should do a similar check if GOOS or GOARCH are unset.

If you decide to go into the check when change option, looking again checkEnvWrite() only does checks for independent variables changes, so I think it can't be leveraged.
In this case, GOOS or GOARCH can't be validated independently but in combination. Making checks here would work only if GOOS or GOARCH are being touched, but not both in the same go env -w (as the example above).

[gopherbot]

Change https://golang.org/cl/194617 mentions this issue: cmd/go: env -w and -u check for invalid GOOS and GOARCH values