Last one wins flag providers (#501)

* Adjusts to last one wins logic for flag provider

* Removed unused schema

* Reverted dotnet feature definition to continue to use FirstOrDefault

src/Microsoft.FeatureManagement/ConfigurationFeatureDefinitionProvider.cs

@@ -172,7 +172,7 @@ private FeatureDefinition GetMicrosoftSchemaFeatureDefinition(string featureName
             IEnumerable<IConfigurationSection> microsoftFeatureDefinitionSections = GetMicrosoftFeatureDefinitionSections();
 
             IConfigurationSection configuration = microsoftFeatureDefinitionSections
-                .FirstOrDefault(section =>
+                .LastOrDefault(section =>
                     string.Equals(section[MicrosoftFeatureManagementFields.Id], featureName, StringComparison.OrdinalIgnoreCase));
 
             if (configuration == null)

tests/Tests.FeatureManagement/DotnetFeatureManagementSchema.json

@@ -13,4 +13,4 @@
       ]
     }
   }
-}
+}

tests/Tests.FeatureManagement/FeatureManagementTest.cs

@@ -427,6 +427,26 @@ public async Task CustomFeatureDefinitionProvider()
 
             Assert.True(called);
         }
+
+        [Fact]
+        public async Task LastFeatureFlagWins()
+        {
+            IConfiguration configuration = new ConfigurationBuilder()
+                .AddJsonFile("appsettings.json")
+                .Build();
+
+            IServiceCollection services = new ServiceCollection();
+
+            services
+                .AddSingleton(configuration)
+                .AddFeatureManagement();
+
+            ServiceProvider serviceProvider = services.BuildServiceProvider();
+
+            IFeatureManager featureManager = serviceProvider.GetRequiredService<IFeatureManager>();
+
+            Assert.True(await featureManager.IsEnabledAsync(Features.DuplicateFlag));
+        }
     }
 
     public class FeatureManagementFeatureFilterGeneralTest

tests/Tests.FeatureManagement/Features.cs

@@ -30,5 +30,6 @@ static class Features
         public const string OnTelemetryTestFeature = "OnTelemetryTestFeature";
         public const string OffTelemetryTestFeature = "OffTelemetryTestFeature";
         public const string ContextualFeatureWithVariant = "ContextualFeatureWithVariant";
+        public const string DuplicateFlag = "DuplicateFlag";
     }
 }

tests/Tests.FeatureManagement/appsettings.json

@@ -530,6 +530,14 @@
           "default_when_enabled": "Big",
           "default_when_disabled": "Small"
         }
+      },
+      {
+        "id": "DuplicateFlag",
+        "enabled": false
+      },
+      {
+        "id": "DuplicateFlag",
+        "enabled": true
       }
     ]
   }