x/build: add test coverage for netgo and osusergo build tags

[bradfitz]

In #24841 we learned that the osusergo build tag resulted in an os/user package that didn't even compile.

We should make sure we have some test or builder coverage for those build tags.

[gopherbot]

Change https://golang.org/cl/106837 mentions this issue: os/user: fix build with "osusergo" build tag

[bradfitz]

The osusergo tag was added in 62f0127 (@kolyshkin)

And it turns out it never worked, even when it was first committed:

bradfitz@gdev:~/go/src$ git reset --hard 62f0127d8104d8266d9a3fb5a87e2f09ec8b6f5b
HEAD is now at 62f0127 os/user: add a way to enforce pure Go implementation

bradfitz@gdev:~/go/src$ ./make.bash 
Building Go cmd/dist using /home/bradfitz/go1.4.
Building Go toolchain1 using /home/bradfitz/go1.4.
Building Go bootstrap cmd/go (go_bootstrap) using Go toolchain1.
Building Go toolchain2 using go_bootstrap and Go toolchain1.
Building Go toolchain3 using go_bootstrap and Go toolchain2.
Building packages and commands for linux/amd64.
---
Installed Go for linux/amd64 in /home/bradfitz/go
Installed commands in /home/bradfitz/go/bin

bradfitz@gdev:~/go/src$ go install --tags=osusergo os/user
# os/user
os/user/getgrouplist_unix.go:32: undefined: maxGroups
os/user/getgrouplist_unix.go:33: undefined: maxGroups

[gopherbot]

Change https://golang.org/cl/107299 mentions this issue: os/user: fix build on darwin with "osusergo" build tag

[gopherbot]

Change https://golang.org/cl/107300 mentions this issue: cmd/dist: test os/user in osusergo mode as well

[kolyshkin]

I am not sure what would be an elegant way of implementing this, but this is what I came up with:

kir@kd:~/git/golang/go/src$ cat os/user/build_test.go 
// Copyright 2018 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package user_test

import (
	"internal/testenv"
	"os"
	"os/exec"
	"testing"
)

// TestBuild checks if the package can be built with the "osusergo" tag set
func TestBuild(t *testing.T) {
	testenv.MustHaveGoBuild(t)

	cmd := exec.Command(testenv.GoToolPath(t), "build", "-tags", "osusergo", ".")
	run(cmd, t)
}

func run(c *exec.Cmd, t *testing.T) {
	t.Helper()
	c.Stdout = os.Stdout
	c.Stderr = os.Stderr
	err := c.Run()
	if err != nil {
		t.Fatal(err)
	}
}

Let me know if this looks decent, and I'll add the same for netgo

[kolyshkin]

And yes, the above test catches the #24841 when I revert the patch manually:

kir@kd:~/git/golang/go/src$ ./race.bash 
Building Go cmd/dist using /usr/lib/go-1.10.
Building Go toolchain1 using /usr/lib/go-1.10.
Building Go bootstrap cmd/go (go_bootstrap) using Go toolchain1.
Building Go toolchain2 using go_bootstrap and Go toolchain1.
Building Go toolchain3 using go_bootstrap and Go toolchain2.
Building packages and commands for linux/amd64.


##### Testing packages.
ok  	archive/tar	1.202s
ok  	archive/zip	1.910s
...skipped...
ok  	os	9.767s
ok  	os/exec	22.864s
ok  	os/signal	18.517s
# os/user
./getgrouplist_unix.go:32: undefined: maxGroups
./getgrouplist_unix.go:33: undefined: maxGroups
--- FAIL: TestBuild (0.22s)
	osusergo_build_test.go:19: exit status 2
FAIL
FAIL	os/user	0.224s
ok  	path	1.007s
ok  	path/filepath	1.021s
...skipped...
ok  	vendor/golang_org/x/text/unicode/norm	1.007s
2018/04/16 10:50:24 Failed: exit status 1

[bradfitz]

@kolyshkin, I had already sent https://golang.org/cl/107300

[gopherbot]

Change https://golang.org/cl/107304 mentions this issue: os/user: fix osusergo build on Solaris