fix: I18NProvider.translate return same as Component.translate (#22363)

The I18NProvider.translate should return the
same as Component.translate when no provider
can be found.

Fixes #19516

Author: caalador

flow-server/src/main/java/com/vaadin/flow/i18n/I18NProvider.java

@@ -20,17 +20,23 @@
 import java.util.List;
 import java.util.Locale;
 import java.util.Map;
+import java.util.Optional;
 import java.util.function.Function;
 import java.util.stream.Collectors;
 
+import org.slf4j.LoggerFactory;
+
+import com.vaadin.flow.di.Instantiator;
 import com.vaadin.flow.internal.LocaleUtil;
+import com.vaadin.flow.server.VaadinService;
 
 /**
  * I18N provider interface for internationalization usage.
  *
  * @since 1.0
  */
 public interface I18NProvider extends Serializable {
+
     /**
      * Get the locales that we have translations for. The first locale should be
      * the default locale.
@@ -137,6 +143,9 @@ static String translate(String key, Object... params) {
     /**
      * Get the translation for key with given locale via {@link I18NProvider}
      * instance retrieved from the current VaadinService.
+     * <p>
+     * If there is no {@link I18NProvider} available or no translation for the
+     * {@code key} it returns an exception string e.g. '!{key}!'.
      *
      * @param locale
      *            locale to use
@@ -145,13 +154,21 @@ static String translate(String key, Object... params) {
      * @param params
      *            parameters used in translation string
      * @return translation for key if found
-     * @throws IllegalStateException
-     *             thrown if no I18NProvider found from the VaadinService
      */
     static String translate(Locale locale, String key, Object... params) {
+        VaadinService vaadinService = VaadinService.getCurrent();
+        if (vaadinService == null) {
+            throw new IllegalStateException(
+                    "I18NProvider is not available as VaadinService is null");
+        }
+        Instantiator instantiator = vaadinService.getInstantiator();
+        if (instantiator == null) {
+            throw new IllegalStateException(
+                    "I18NProvider is not available as Instantiator is null");
+        }
+
         return LocaleUtil.getI18NProvider()
-                .orElseThrow(() -> new IllegalStateException(
-                        "I18NProvider is not available via current VaadinService. VaadinService, Instantiator or I18NProvider is null."))
-                .getTranslation(key, locale, params);
+                .map(i18n -> i18n.getTranslation(key, locale, params))
+                .orElseGet(() -> "!{" + key + "}!");
     }
 }

flow-server/src/test/java/com/vaadin/flow/i18n/DefaultInstantiatorI18NTest.java

@@ -209,14 +209,17 @@ protected ClassLoader getClassLoader() {
     }
 
     @Test
-    public void translate_withoutInstantiator_throwsIllegalStateException() {
+    public void translate_withoutProvider_returnsKey() {
         VaadinService service = Mockito.mock(VaadinService.class);
         VaadinService.setCurrent(service);
 
-        Assert.assertThrows(
-                "Should throw exception without Instantiator in VaadinService",
-                IllegalStateException.class,
-                () -> I18NProvider.translate("foo.bar"));
+        DefaultInstantiator defaultInstantiator = new DefaultInstantiator(
+                service);
+        Mockito.when(service.getInstantiator()).thenReturn(defaultInstantiator);
+
+        Assert.assertEquals(
+                "Should return the key with !{}! to show no translation available",
+                "!{foo.bar}!", I18NProvider.translate("foo.bar"));
     }
 
     @Test

flow-server/src/test/java/com/vaadin/flow/server/I18NProviderTest.java

@@ -99,6 +99,16 @@ public void translate_calls_provider()
                 "!foo.bar!", I18NProvider.translate("foo.bar"));
     }
 
+    @Test
+    public void translate_withoutProvider_returnsKey()
+            throws ServletException, ServiceException {
+        initServletAndService(config);
+
+        Assert.assertEquals(
+                "Should return the key with !{}! to show no translation available",
+                "!{foo.bar}!", I18NProvider.translate("foo.bar"));
+    }
+
     @Test
     public void translate_withoutVaadinService_throwIllegalStateException()
             throws ServletException, ServiceException {
@@ -115,6 +125,28 @@ public void translate_withoutVaadinService_throwIllegalStateException()
                 () -> I18NProvider.translate("foo.bar"));
     }
 
+    @Test
+    public void translate_withoutInstantiator_throwIllegalStateException()
+            throws ServletException, ServiceException {
+        config.setApplicationOrSystemProperty(InitParameters.I18N_PROVIDER,
+                TestProvider.class.getName());
+
+        initServletAndService(config);
+        service = new MockVaadinServletService(config) {
+            @Override
+            public Instantiator getInstantiator() {
+                return null;
+            }
+        };
+
+        VaadinService.setCurrent(service);
+
+        Assert.assertThrows(
+                "Should throw exception without active VaadinService",
+                IllegalStateException.class,
+                () -> I18NProvider.translate("foo.bar"));
+    }
+
     @Before
     public void initState()
             throws NoSuchFieldException, IllegalAccessException {