Throw exception if feature management schemas are mixed to avoid unintentionally hiding feature flags.

src/Microsoft.FeatureManagement/ConfigurationDynamicFeatureDefinitionProvider.cs

@@ -19,8 +19,8 @@ namespace Microsoft.FeatureManagement
     /// </summary>
     sealed class ConfigurationDynamicFeatureDefinitionProvider : IDynamicFeatureDefinitionProvider, IDisposable
     {
+        public const string DynamicFeatureDefinitionsSectionName = "DynamicFeatures";
         private const string FeatureManagementSectionName = "FeatureManagement";
-        private const string DynamicFeatureDefinitionsSectionName= "DynamicFeatures";
         private const string FeatureVariantsSectionName = "Variants";
         private readonly IConfiguration _configuration;
         private readonly ConcurrentDictionary<string, DynamicFeatureDefinition> _dynamicFeatureDefinitions;

src/Microsoft.FeatureManagement/ConfigurationFeatureFlagDefinitionProvider.cs

@@ -186,6 +186,18 @@ private IEnumerable<IConfigurationSection> GetFeatureFlagDefinitionSections()
 
             IConfigurationSection featureFlagsSection = featureManagementChildren.FirstOrDefault(s => s.Key == FeatureFlagDefinitionsSectionName);
 
+            //
+            // Check for mixed schema to avoid confusing scenario where feature flags defined in separate sources with different schemas don't mix.
+            if (featureFlagsSection != null &&
+                featureManagementChildren.Any(section =>
+                    !section.Key.Equals(FeatureFlagDefinitionsSectionName) &&
+                    !section.Key.Equals(ConfigurationDynamicFeatureDefinitionProvider.DynamicFeatureDefinitionsSectionName)))
+            {
+                throw new FeatureManagementException(
+                    FeatureManagementError.InvalidConfiguration,
+                    "Detected feature flags defined using different feature management schemas.");
+            }
+
             //
             // Support backward compatability where feature flag definitions were directly under the feature management section
             return featureFlagsSection == null ?

src/Microsoft.FeatureManagement/FeatureManagementError.cs

@@ -61,6 +61,11 @@ public enum FeatureManagementError
         /// <summary>
         /// A dynamic feature does not have a default feature variant configured.
         /// </summary>
-        MissingDefaultFeatureVariant
+        MissingDefaultFeatureVariant,
+
+        /// <summary>
+        /// A configuration error is present in the feature management system.
+        /// </summary>
+        InvalidConfiguration
     }
 }