Fix Configuration to throw with ErrorOnUnknownConfiguration option (#110209)

* Fix Configuration to throw with ErrorOnUnknownConfiguration option

* Fix the fired Debug.Assert

* address the feedback

Author: tarekgh

src/libraries/Microsoft.Extensions.Configuration.Binder/src/ConfigurationBinder.cs

@@ -465,9 +465,23 @@ private static void BindInstance(
             }
             else
             {
-                if (isParentCollection && bindingPoint.Value is null && string.IsNullOrEmpty(configValue))
+                // Reaching this point indicates that the configuration section is a leaf node with a string value.
+                // Typically, configValue will be an empty string if the value in the configuration is empty or null.
+                // While configValue could be any other string, we already know it cannot be converted to the required type, as TryConvertValue has already failed.
+
+                if (!string.IsNullOrEmpty(configValue))
                 {
-                    // If we don't have an instance, try to create one
+                    // If we have a value, but no children, we can't bind it to anything
+                    // We already tried calling TryConvertValue and couldn't convert the configuration value to the required type.
+                    if (options.ErrorOnUnknownConfiguration)
+                    {
+                        Debug.Assert(section is not null);
+                        throw new InvalidOperationException(SR.Format(SR.Error_FailedBinding, section.Path, type));
+                    }
+                }
+                else if (isParentCollection && bindingPoint.Value is null)
+                {
+                    // Try to create the default instance of the type
                     bindingPoint.TrySetValue(CreateInstance(type, config, options, out _));
                 }
             }
@@ -498,8 +512,6 @@ private static object CreateInstance(
             BinderOptions options,
             out ParameterInfo[]? constructorParameters)
         {
-            Debug.Assert(!type.IsArray);
-
             constructorParameters = null;
 
             if (type.IsInterface || type.IsAbstract)

src/libraries/Microsoft.Extensions.Configuration.Binder/tests/Common/ConfigurationBinderTests.cs

@@ -2815,5 +2815,22 @@ public void CanGetEnumerableNotCollection()
             Assert.True(result.Enabled);
             Assert.Equal(new [] { "new", "class", "rosebud"}, result.Keywords);
         }
+
+#if !BUILDING_SOURCE_GENERATOR_TESTS
+        [Fact]
+        public void EnsureThrowingWithCollectionAndErrorOnUnknownConfigurationOption()
+        {
+            var configuration = new ConfigurationBuilder().AddInMemoryCollection(new Dictionary<string, string?> { ["Values:Monday"] = "not-an-array-of-string" }).Build();
+            Assert.Throws<InvalidOperationException>(() => configuration.Get<TestSettings>(options => options.ErrorOnUnknownConfiguration = true));
+
+            configuration = new ConfigurationBuilder().AddInMemoryCollection(new Dictionary<string, string?> { ["Values:Monday"] = "" }).Build();
+            Assert.Throws<InvalidOperationException>(() => configuration.Get<TestSettings>(options => options.ErrorOnUnknownConfiguration = true));
+
+            configuration = new ConfigurationBuilder().AddInMemoryCollection(new Dictionary<string, string?> { ["Values:Monday"] = null }).Build();
+            Assert.Throws<InvalidOperationException>(() => configuration.Get<TestSettings>(options => options.ErrorOnUnknownConfiguration = true));
+        }
+
+        internal class TestSettings { public Dictionary<DayOfWeek, string[]> Values { get; init; } = []; }
+#endif
     }
 }