better handling of path differences for MSI installers (#7035)

Related to #7036, Tested in:

- [x] macOS via `fleetctl package --type=msi` (non-native)
- [x] Linux native via `docker run -v "$(pwd)" fleetdm/fleetctl package --type=msi` (native)
- [x] Windows via `fleetctl pacakge --type=msi` (thanks to @edwardsb) (non-native)

changes/issue-7036-windows-msi

@@ -0,0 +1 @@
+* Fixed a bug preventing `.msi` installers to be generated on Windows machines.

orbit/pkg/packaging/wix/wix.go

@@ -7,26 +7,12 @@ import (
 	"fmt"
 	"os"
 	"os/exec"
-	"strings"
 )
 
 const (
-	directoryReference   = "ORBITROOT"
-	linuxPathSeparator   = "/"
-	windowsPathSeparator = "\\"
+	directoryReference = "ORBITROOT"
 )
 
-// windowsJoin returns the result of replacing each slash ('/') character in
-// each path with a Windows separator character ('\') and joining them using
-// the Windows separator character.
-//
-// We can't use filepath.FromSlash because this func is run in a *nix
-// machine.
-func windowsJoin(paths ...string) string {
-	s := strings.Join(paths, windowsPathSeparator)
-	return strings.ReplaceAll(s, linuxPathSeparator, windowsPathSeparator)
-}
-
 // Heat runs the WiX Heat command on the provided directory.
 //
 // The Heat command creates XML fragments allowing WiX to include the entire
@@ -39,14 +25,14 @@ func Heat(path string, native bool) error {
 		args = append(
 			args,
 			"docker", "run", "--rm", "--platform", "linux/amd64",
-			"--volume", path+":"+path, // mount volume
+			"--volume", path+":/wix", // mount volume
 			"fleetdm/wix:latest", // image name
 		)
 	}
 
 	args = append(args,
-		"heat", "dir", windowsJoin(path, "root"), // command
-		"-out", windowsJoin(path, "heat.wxs"),
+		"heat", "dir", "root", // command
+		"-out", "heat.wxs",
 		"-gg", "-g1", // generate UUIDs (required by wix)
 		"-cg", "OrbitFiles", // set ComponentGroup name
 		"-scom", "-sfrag", "-srd", "-sreg", // suppress unneccesary generated items
@@ -57,6 +43,10 @@ func Heat(path string, native bool) error {
 	cmd := exec.Command(args[0], args[1:]...)
 	cmd.Stdout, cmd.Stderr = os.Stdout, os.Stderr
 
+	if native {
+		cmd.Dir = path
+	}
+
 	if err := cmd.Run(); err != nil {
 		return fmt.Errorf("heat failed: %w", err)
 	}
@@ -75,14 +65,13 @@ func Candle(path string, native bool) error {
 		args = append(
 			args,
 			"docker", "run", "--rm", "--platform", "linux/amd64",
-			"--volume", path+":"+path, // mount volume
+			"--volume", path+":/wix", // mount volume
 			"fleetdm/wix:latest", // image name
 		)
 	}
 
 	args = append(args,
-		"candle", windowsJoin(path, "heat.wxs"), windowsJoin(path, "main.wxs"), // command
-		"-out", windowsJoin(path, ""),
+		"candle", "heat.wxs", "main.wxs", // command
 		"-ext", "WixUtilExtension",
 		"-arch", "x64",
 	)
@@ -90,6 +79,10 @@ func Candle(path string, native bool) error {
 	cmd := exec.Command(args[0], args[1:]...)
 	cmd.Stdout, cmd.Stderr = os.Stdout, os.Stderr
 
+	if native {
+		cmd.Dir = path
+	}
+
 	if err := cmd.Run(); err != nil {
 		return fmt.Errorf("candle failed: %w", err)
 	}
@@ -108,22 +101,26 @@ func Light(path string, native bool) error {
 		args = append(
 			args,
 			"docker", "run", "--rm", "--platform", "linux/amd64",
-			"--volume", path+":"+path, // mount volume
+			"--volume", path+":/wix", // mount volume
 			"fleetdm/wix:latest", // image name
 		)
 	}
 
 	args = append(args,
-		"light", windowsJoin(path, "heat.wixobj"), windowsJoin(path, "main.wixobj"), // command
+		"light", "heat.wixobj", "main.wixobj", // command
 		"-ext", "WixUtilExtension",
-		"-b", windowsJoin(path, "root"), // Set directory for finding heat files
-		"-out", windowsJoin(path, "orbit.msi"),
+		"-b", "root", // Set directory for finding heat files
+		"-out", "orbit.msi",
 		"-sval", // skip validation (otherwise Wine crashes)
 	)
 
 	cmd := exec.Command(args[0], args[1:]...)
 	cmd.Stdout, cmd.Stderr = os.Stdout, os.Stderr
 
+	if native {
+		cmd.Dir = path
+	}
+
 	if err := cmd.Run(); err != nil {
 		return fmt.Errorf("light failed: %w", err)
 	}

orbit/pkg/packaging/wix/wix_test.go

@@ -1,23 +0,0 @@
-package wix
-
-import (
-	"testing"
-
-	"github.com/stretchr/testify/require"
-)
-
-func TestWindowsJoin(t *testing.T) {
-	cases := []struct {
-		in  []string
-		out string
-	}{
-		{[]string{"one\\two", "three"}, "one\\two\\three"},
-		{[]string{"one/two/three", "four.txt"}, "one\\two\\three\\four.txt"},
-		{[]string{"one", "two", "three"}, "one\\two\\three"},
-		{[]string{"one/two/three", "four/five.txt"}, "one\\two\\three\\four\\five.txt"},
-	}
-
-	for _, c := range cases {
-		require.Equal(t, c.out, windowsJoin(c.in...))
-	}
-}