refactor(testrun): defer the java preflight check to the physical-device path

internal/testrun/preflight.go

@@ -41,18 +41,30 @@ func runPreflight(ctx context.Context, platform string, check preflightFunc) err
 		}
 		return nil
 	case "ios":
+		// Simulator runs drive the native companion and need no JVM. The java
+		// requirement is deferred to the physical-device path in buildDriver.
 		if err := check("xcrun"); err != nil {
 			return preflightFailure("ios", err)
 		}
-		if err := check("java"); err != nil {
-			return preflightFailure("ios", err)
-		}
 		return nil
 	default:
 		return fmt.Errorf("preflight: unknown platform %q", platform)
 	}
 }
 
+// preflightDevice runs the extra host checks the JVM sidecar path needs once we
+// know a run targets a physical iOS device. Android already requires java in
+// the top-level Preflight, so this only matters for ios.
+func preflightDevice(platform string) error {
+	if platform != "ios" {
+		return nil
+	}
+	if err := preflightCheck("java"); err != nil {
+		return preflightFailure("ios", err)
+	}
+	return nil
+}
+
 func preflightFailure(platform string, cause error) error {
 	return fmt.Errorf(
 		"preflight: %w\nrun `sanderling doctor --platform=%s` for full host-readiness checks",

internal/testrun/preflight_test.go

@@ -49,7 +49,7 @@ func TestPreflight_AndroidNeedsAdbAndJava(t *testing.T) {
 	}
 }
 
-func TestPreflight_iOSNeedsXcrunAndJava(t *testing.T) {
+func TestPreflight_iOSNeedsXcrun(t *testing.T) {
 	check := func(name string) error {
 		if name == "xcrun" {
 			return errors.New("xcrun not found")
@@ -65,6 +65,25 @@ func TestPreflight_iOSNeedsXcrunAndJava(t *testing.T) {
 	}
 }
 
+func TestPreflight_iOSDoesNotRequireJava(t *testing.T) {
+	checked := []string{}
+	check := func(name string) error {
+		checked = append(checked, name)
+		if name == "java" {
+			return errors.New("java not found")
+		}
+		return nil
+	}
+	if err := runPreflight(context.Background(), "ios", check); err != nil {
+		t.Fatalf("ios preflight should pass without java, got %v", err)
+	}
+	for _, name := range checked {
+		if name == "java" {
+			t.Errorf("ios preflight must not check java; simulator runs need no JVM")
+		}
+	}
+}
+
 func TestPreflight_AllOK(t *testing.T) {
 	check := func(name string) error { return nil }
 	for _, platform := range []string{"web", "android", "ios"} {
@@ -74,6 +93,14 @@ func TestPreflight_AllOK(t *testing.T) {
 	}
 }
 
+func TestPreflightDevice_NonIosIsNoop(t *testing.T) {
+	for _, platform := range []string{"web", "android"} {
+		if err := preflightDevice(platform); err != nil {
+			t.Errorf("%s: preflightDevice should be a no-op, got %v", platform, err)
+		}
+	}
+}
+
 func TestPreflight_UnknownPlatform(t *testing.T) {
 	check := func(string) error { return nil }
 	if err := runPreflight(context.Background(), "fuchsia", check); err == nil {