From 28464ae4ee9685df441f37f7cd61031ebb981b85 Mon Sep 17 00:00:00 2001
From: Jimmy Campbell <jimmyca@microsoft.com>
Date: Wed, 1 Sep 2021 11:31:49 -0700
Subject: [PATCH 1/2] Added option to throw for missing features.

---
 .../FeatureManagementError.cs                 |  7 +++++-
 .../FeatureManagementOptions.cs               |  6 +++++
 .../FeatureManager.cs                         | 13 ++++++++++
 .../FeatureManagement.cs                      | 25 +++++++++++++++++++
 4 files changed, 50 insertions(+), 1 deletion(-)

diff --git a/src/Microsoft.FeatureManagement/FeatureManagementError.cs b/src/Microsoft.FeatureManagement/FeatureManagementError.cs
index a1e3319f..1cdb9eed 100644
--- a/src/Microsoft.FeatureManagement/FeatureManagementError.cs
+++ b/src/Microsoft.FeatureManagement/FeatureManagementError.cs
@@ -16,6 +16,11 @@ public enum FeatureManagementError
         /// <summary>
         /// A feature filter configured for the feature being evaluated is an ambiguous reference to multiple registered feature filters.
         /// </summary>
-        AmbiguousFeatureFilter
+        AmbiguousFeatureFilter,
+
+        /// <summary>
+        /// A feature that was requested for evaluation was not found.
+        /// </summary>
+        MissingFeature
     }
 }
diff --git a/src/Microsoft.FeatureManagement/FeatureManagementOptions.cs b/src/Microsoft.FeatureManagement/FeatureManagementOptions.cs
index 9322934e..23c2b6c3 100644
--- a/src/Microsoft.FeatureManagement/FeatureManagementOptions.cs
+++ b/src/Microsoft.FeatureManagement/FeatureManagementOptions.cs
@@ -13,5 +13,11 @@ public class FeatureManagementOptions
         /// If missing feature filters are not ignored an exception will be thrown when attempting to evaluate a feature that depends on a missing feature filter.
         /// </summary>
         public bool IgnoreMissingFeatureFilters { get; set; }
+
+        /// <summary>
+        /// Controls the behavior of feature evaluation when the target feature is missing.
+        /// If missing features are not ignored an exception will be thrown when attempting to evaluate them.
+        /// </summary>
+        public bool IgnoreMissingFeatures { get; set; } = true;
     }
 }
diff --git a/src/Microsoft.FeatureManagement/FeatureManager.cs b/src/Microsoft.FeatureManagement/FeatureManager.cs
index 25873f50..74bd10ab 100644
--- a/src/Microsoft.FeatureManagement/FeatureManager.cs
+++ b/src/Microsoft.FeatureManagement/FeatureManager.cs
@@ -141,6 +141,19 @@ private async Task<bool> IsEnabledAsync<TContext>(string feature, TContext appCo
                     }
                 }
             }
+            else
+            {
+                string errorMessage = $"The feature declaration for the feature '{feature}' was not found.";
+
+                if (!_options.IgnoreMissingFeatures)
+                {
+                    throw new FeatureManagementException(FeatureManagementError.MissingFeatureFilter, errorMessage);
+                }
+                else
+                {
+                    _logger.LogWarning(errorMessage);
+                }
+            }
 
             foreach (ISessionManager sessionManager in _sessionManagers)
             {
diff --git a/tests/Tests.FeatureManagement/FeatureManagement.cs b/tests/Tests.FeatureManagement/FeatureManagement.cs
index e30888e4..d7e85366 100644
--- a/tests/Tests.FeatureManagement/FeatureManagement.cs
+++ b/tests/Tests.FeatureManagement/FeatureManagement.cs
@@ -485,6 +485,31 @@ public async Task SwallowsExceptionForMissingFeatureFilter()
             Assert.False(isEnabled);
         }
 
+        [Fact]
+        public async Task ThrowsForMissingFeatures()
+        {
+            IConfiguration config = new ConfigurationBuilder().AddJsonFile("appsettings.json").Build();
+
+            var services = new ServiceCollection();
+
+            services
+                .Configure<FeatureManagementOptions>(options =>
+                {
+                    options.IgnoreMissingFeatures = false;
+                });
+
+            services
+                .AddSingleton(config)
+                .AddFeatureManagement();
+
+            ServiceProvider serviceProvider = services.BuildServiceProvider();
+
+            IFeatureManager featureManager = serviceProvider.GetRequiredService<IFeatureManager>();
+
+            FeatureManagementException fme = await Assert.ThrowsAsync<FeatureManagementException>(() =>
+                featureManager.IsEnabledAsync("NonExistentFeature"));
+        }
+
         [Fact]
         public async Task CustomFeatureDefinitionProvider()
         {

From 485371b1eefcc813cc90e814c871949b81aea10c Mon Sep 17 00:00:00 2001
From: Jimmy Campbell <jimmyca@microsoft.com>
Date: Wed, 1 Sep 2021 15:04:19 -0700
Subject: [PATCH 2/2] Add default value documentation for feature management
 options.

---
 src/Microsoft.FeatureManagement/FeatureManagementOptions.cs | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/src/Microsoft.FeatureManagement/FeatureManagementOptions.cs b/src/Microsoft.FeatureManagement/FeatureManagementOptions.cs
index 23c2b6c3..e425c054 100644
--- a/src/Microsoft.FeatureManagement/FeatureManagementOptions.cs
+++ b/src/Microsoft.FeatureManagement/FeatureManagementOptions.cs
@@ -11,12 +11,14 @@ public class FeatureManagementOptions
         /// <summary>
         /// Controls the behavior of feature evaluation when dependent feature filters are missing.
         /// If missing feature filters are not ignored an exception will be thrown when attempting to evaluate a feature that depends on a missing feature filter.
+        /// The default value is false.
         /// </summary>
         public bool IgnoreMissingFeatureFilters { get; set; }
 
         /// <summary>
         /// Controls the behavior of feature evaluation when the target feature is missing.
         /// If missing features are not ignored an exception will be thrown when attempting to evaluate them.
+        /// The default value is true.
         /// </summary>
         public bool IgnoreMissingFeatures { get; set; } = true;
     }