fix: add warnings for unsupported feature flags in properties file (#…

…18672)

flow-server/src/main/java/com/vaadin/experimental/FeatureFlags.java

@@ -82,6 +82,8 @@ public class FeatureFlags implements Serializable {
 
     private ApplicationConfiguration configuration;
 
+    private boolean isPropertiesFileChecked = false;
+
     /**
      * Generate FeatureFlags with given lookup data.
      *
@@ -208,6 +210,11 @@ void loadProperties(InputStream propertiesStream) {
 
             if (propertiesStream != null) {
                 props.load(propertiesStream);
+                // Check once if there are unsupported feature flags in the file
+                if (!isPropertiesFileChecked) {
+                    checkForUnsupportedFeatureFlags(props);
+                    isPropertiesFileChecked = true;
+                }
             }
             for (Feature f : features) {
                 // Allow users to override a feature flag with a system property
@@ -346,4 +353,13 @@ public String getEnableHelperMessage(Feature feature) {
     private Logger getLogger() {
         return LoggerFactory.getLogger(FeatureFlags.class);
     }
+
+    private void checkForUnsupportedFeatureFlags(Properties props) {
+        for (Object property : props.keySet()) {
+            if (features.stream()
+                    .noneMatch(feature -> getPropertyName(feature.getId()).equals(property))) {
+                getLogger().warn("Unsupported feature flag is present: {}", property);
+            }
+        }
+    }
 }

flow-server/src/test/java/com/vaadin/experimental/FeatureFlagsTest.java

@@ -32,7 +32,9 @@
 import org.junit.Rule;
 import org.junit.Test;
 import org.junit.rules.TemporaryFolder;
+import org.mockito.MockedStatic;
 import org.mockito.Mockito;
+import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
 import com.vaadin.flow.di.Lookup;
@@ -405,6 +407,43 @@ public void get_concurrentAccess_vaadinContextLock_noDeadlock()
                 latch.await(1, TimeUnit.SECONDS));
     }
 
+    @Test
+    public void propertiesFileCheckedForUnsupportedFeatureFlags() throws IOException {
+        Logger mockedLogger = Mockito.mock(Logger.class);
+
+        try (MockedStatic<LoggerFactory> context = Mockito.mockStatic(LoggerFactory.class)) {
+            context.when(() -> LoggerFactory.getLogger(FeatureFlags.class))
+                    .thenReturn(mockedLogger);
+
+            createFeatureFlagsFile(
+                    "com.vaadin.experimental.unsupportedFeature=true\ncom.vaadin.experimental.exampleFeatureFlag=true\n");
+            featureFlags.loadProperties();
+
+            Mockito.verify(mockedLogger, Mockito.never())
+                    .warn("Unsupported feature flag is present: {}", "com.vaadin.experimental.exampleFeatureFlag");
+            Mockito.verify(mockedLogger, Mockito.times(1))
+                    .warn("Unsupported feature flag is present: {}", "com.vaadin.experimental.unsupportedFeature");
+        }
+    }
+
+    @Test
+    public void propertiesFileCheckForUnsupportedFeatureFlagsRanOnlyOnce() throws IOException {
+        Logger mockedLogger = Mockito.mock(Logger.class);
+
+        try (MockedStatic<LoggerFactory> context = Mockito.mockStatic(LoggerFactory.class)) {
+            context.when(() -> LoggerFactory.getLogger(FeatureFlags.class))
+                    .thenReturn(mockedLogger);
+
+            createFeatureFlagsFile(
+                    "com.vaadin.experimental.unsupportedFeature=true\n");
+            featureFlags.loadProperties();
+            featureFlags.loadProperties();
+
+            Mockito.verify(mockedLogger, Mockito.times(1))
+                    .warn("Unsupported feature flag is present: {}", "com.vaadin.experimental.unsupportedFeature");
+        }
+    }
+
     private boolean hasUsageStatsEntry(String name) {
         return UsageStatistics.getEntries()
                 .filter(entry -> entry.getName().equals(name)).findFirst()