fix: do not use only hardcoded "go"

builder.go

@@ -101,13 +101,13 @@ func (b Builder) Build(ctx context.Context, outputFile string) error {
 	log.Println("[INFO] Building Caddy")
 
 	// tidy the module to ensure go.mod and go.sum are consistent with the module prereq
-	tidyCmd := buildEnv.newCommand("go", "mod", "tidy")
+	tidyCmd := buildEnv.newCommand(GetGo(), "mod", "tidy")
 	if err := buildEnv.runCommand(ctx, tidyCmd, b.TimeoutGet); err != nil {
 		return err
 	}
 
 	// compile
-	cmd := buildEnv.newCommand("go", "build",
+	cmd := buildEnv.newCommand(GetGo(), "build",
 		"-o", absOutputFile,
 	)
 	if b.Debug {

cmd/main.go

@@ -177,7 +177,7 @@ func runDev(ctx context.Context, args []string) error {
 	// and since this tool is a carry-through for the user's actual
 	// go.mod, we need to transfer their replace directives through
 	// to the one we're making
-	cmd := exec.Command("go", "list", "-m", "-json", "all")
+	cmd := exec.Command(xcaddy.GetGo(), "list", "-m", "-json", "all")
 	cmd.Stderr = os.Stderr
 	out, err := cmd.Output()
 	if err != nil {

environment.go

@@ -100,7 +100,7 @@ func (b Builder) newEnvironment(ctx context.Context) (*environment, error) {
 
 	// initialize the go module
 	log.Println("[INFO] Initializing Go module")
-	cmd := env.newCommand("go", "mod", "init", "caddy")
+	cmd := env.newCommand(GetGo(), "mod", "init", "caddy")
 	err = env.runCommand(ctx, cmd, 10*time.Second)
 	if err != nil {
 		return nil, err
@@ -110,7 +110,7 @@ func (b Builder) newEnvironment(ctx context.Context) (*environment, error) {
 	replaced := make(map[string]string)
 	for _, r := range b.Replacements {
 		log.Printf("[INFO] Replace %s => %s", r.Old.String(), r.New.String())
-		cmd := env.newCommand("go", "mod", "edit",
+		cmd := env.newCommand(GetGo(), "mod", "edit",
 			"-replace", fmt.Sprintf("%s=%s", r.Old.Param(), r.New.Param()))
 		err := env.runCommand(ctx, cmd, 10*time.Second)
 		if err != nil {
@@ -263,9 +263,9 @@ func (env environment) execGoGet(ctx context.Context, modulePath, moduleVersion,
 	// distinct argument, so we're using an if statement to avoid it.
 	var cmd *exec.Cmd
 	if caddy != "" {
-		cmd = env.newCommand("go", "get", "-d", "-v", mod, caddy)
+		cmd = env.newCommand(GetGo(), "get", "-d", "-v", mod, caddy)
 	} else {
-		cmd = env.newCommand("go", "get", "-d", "-v", mod)
+		cmd = env.newCommand(GetGo(), "get", "-d", "-v", mod)
 	}
 
 	return env.runCommand(ctx, cmd, env.timeoutGoGet)

platforms.go

@@ -30,7 +30,7 @@ type Platform struct {
 // SupportedPlatforms runs `go tool dist list` to make
 // a list of possible build targets.
 func SupportedPlatforms() ([]Compile, error) {
-	out, err := exec.Command("go", "tool", "dist", "list", "-json").Output()
+	out, err := exec.Command(GetGo(), "tool", "dist", "list", "-json").Output()
 	if err != nil {
 		return nil, err
 	}

sdk.go

@@ -0,0 +1,11 @@
+package xcaddy
+
+import "os"
+
+func GetGo() string {
+	sdk := os.Getenv("XCADDY_SDK")
+	if sdk == "" {
+		return "go"
+	}
+	return sdk
+}