Add ForceRunInDir()

This helper allows the caller to run a command in a given directory,
and panic on failure.

tools/runner/serial.go

@@ -32,6 +32,14 @@ func ForceRun(exe string, args ...string) {
 	d.Chk.NoError(err)
 }
 
+// ForceRunInDir runs 'exe [args...]' in the given directory, and d.Chk()s on failure. Inherits the environment of the current process.
+func ForceRunInDir(dir, exe string, args ...string) {
+	info, err := os.Stat(dir)
+	d.Exp.NoError(err, "Can't stat %s", dir)
+	d.Exp.True(info.IsDir(), "%s must be a path to a directory.", dir)
+	d.Chk.NoError(runEnvDir(os.Stdout, os.Stderr, Env{}, dir, exe, args...))
+}
+
 // runEnvDir 'exe [args...]' in dir with the environment env overlaid on that of the current process. If dir == "", use the current working directory.
 func runEnvDir(out, err io.Writer, env Env, dir, exe string, args ...string) error {
 	cmd := exec.Command(exe, args...)

tools/runner/serial_test.go

@@ -3,6 +3,7 @@ package runner
 import (
 	"bytes"
 	"fmt"
+	"io"
 	"io/ioutil"
 	"os"
 	"path/filepath"
@@ -42,6 +43,34 @@ func (suite *SerialRunnerTestSuite) TearDownTest() {
 	os.Remove(suite.dir)
 }
 
+func (suite *SerialRunnerTestSuite) TestForceRunInDir() {
+	scriptPath := filepath.Join(suite.dir, buildFileBasename)
+	suite.makeTestBuildFile(scriptPath, []string{"print os.getcwd()"})
+
+	old := os.Stdout // keep backup of the real stdout
+	r, w, err := os.Pipe()
+	suite.NoError(err)
+	os.Stdout = w
+	defer func() { os.Stdout = old }()
+	defer r.Close()
+
+	outC := make(chan string)
+	// copy the output in a separate goroutine so printing can't block indefinitely
+	go func() {
+		buf := &bytes.Buffer{}
+		io.Copy(buf, r)
+		outC <- buf.String()
+	}()
+
+	ForceRunInDir(suite.dir, "python", scriptPath)
+
+	w.Close()
+	out := strings.TrimSpace(<-outC)
+	actualSuiteDir, err := filepath.EvalSymlinks(suite.dir)
+	suite.NoError(err)
+	suite.Equal(actualSuiteDir, out)
+}
+
 func (suite *SerialRunnerTestSuite) TestEnvVars() {
 	makeEnvVarPrintBuildFile := func(path, varname string) {
 		fmtStatement := fmt.Sprintf(`print os.environ['%s']`, varname)