Add IsAvailable.

internal/zenutil/run_unix.go

@@ -8,12 +8,16 @@ import (
 	"os"
 	"os/exec"
 	"strconv"
+	"sync"
 	"syscall"
 )
 
-var tool, path string
+var (
+	tool, path string
+	pathOnce   sync.Once
+)
 
-func init() {
+func initPath() {
 	for _, tool = range [3]string{"qarma", "zenity", "matedialog"} {
 		path, _ = exec.LookPath(tool)
 		if path != "" {
@@ -23,8 +27,15 @@ func init() {
 	tool = "zenity"
 }
 
+// IsAvailable is internal.
+func IsAvailable() bool {
+	pathOnce.Do(initPath)
+	return path != ""
+}
+
 // Run is internal.
 func Run(ctx context.Context, args []string) ([]byte, error) {
+	pathOnce.Do(initPath)
 	if Command && path != "" {
 		if Timeout > 0 {
 			args = append(args, "--timeout", strconv.Itoa(Timeout))
@@ -44,6 +55,7 @@ func Run(ctx context.Context, args []string) ([]byte, error) {
 
 // RunProgress is internal.
 func RunProgress(ctx context.Context, max int, extra *string, args []string) (*progressDialog, error) {
+	pathOnce.Do(initPath)
 	if Command && path != "" {
 		if Timeout > 0 {
 			args = append(args, "--timeout", strconv.Itoa(Timeout))

internal/zenutil/run_unix_test.go

@@ -41,7 +41,7 @@ func TestRunProgress(t *testing.T) {
 }
 
 func skip(err error) (bool, error) {
-	if _, ok := err.(*exec.Error); ok {
+	if _, ok := err.(*exec.Error); ok && !IsAvailable() {
 		// zenity was not found in path
 		return true, err
 	}

zenity.go

@@ -30,6 +30,12 @@ const ErrExtraButton = zenutil.ErrExtraButton
 // ErrUnsupported is returned when a combination of options is not supported.
 const ErrUnsupported = zenutil.ErrUnsupported
 
+// IsAvailable reports whether dependencies of the package are installed.
+// It always returns true on Windows and macOS.
+func IsAvailable() bool {
+	return isAvailable()
+}
+
 type options struct {
 	// General options
 	title         *string
@@ -182,6 +188,16 @@ func WindowIcon(icon any) Option {
 	return funcOption(func(o *options) { o.windowIcon = icon })
 }
 
+// Attach returns an Option to set the parent window to attach to.
+//
+// Attach accepts:
+//   - a window id (int) on Unix
+//   - a window handle (~uintptr) on Windows
+//   - an application name (string) or process id (int) on macOS
+func Attach(id any) Option {
+	return attach(id)
+}
+
 // Modal returns an Option to set the modal hint.
 func Modal() Option {
 	return funcOption(func(o *options) { o.modal = true })

zenity_darwin.go

@@ -1,12 +1,8 @@
 package zenity
 
-// Attach returns an Option to set the parent window to attach to.
-//
-// Attach accepts:
-//   - a window id (int) on Unix
-//   - a window handle (~uintptr) on Windows
-//   - an application name (string) or process id (int) on macOS
-func Attach(id any) Option {
+func isAvailable() bool { return true }
+
+func attach(id any) Option {
 	switch id.(type) {
 	case int, string:
 	default:

zenity_unix.go

@@ -2,12 +2,10 @@
 
 package zenity
 
-// Attach returns an Option to set the parent window to attach to.
-//
-// Attach accepts:
-//   - a window id (int) on Unix
-//   - a window handle (~uintptr) on Windows
-//   - an application name (string) or process id (int) on macOS
-func Attach(id int) Option {
-	return funcOption(func(o *options) { o.attach = id })
+import "github.com/ncruces/zenity/internal/zenutil"
+
+func isAvailable() bool { return zenutil.IsAvailable() }
+
+func attach(id any) Option {
+	return funcOption(func(o *options) { o.attach = id.(int) })
 }

zenity_windows.go

@@ -6,13 +6,9 @@ import (
 	"github.com/ncruces/zenity/internal/win"
 )
 
-// Attach returns an Option to set the parent window to attach to.
-//
-// Attach accepts:
-//   - a window id (int) on Unix
-//   - a window handle (~uintptr) on Windows
-//   - an application name (string) or process id (int) on macOS
-func Attach(id any) Option {
+func isAvailable() bool { return true }
+
+func attach(id any) Option {
 	if v := reflect.ValueOf(id); v.Kind() == reflect.Uintptr {
 		id = win.HWND(uintptr(v.Uint()))
 	} else {