Add COnfigurationIgnoreAttribute by rosebyte · Pull Request #126396 · dotnet/runtime

rosebyte · 2026-04-01T06:25:15Z

Add ConfigurationIgnoreAttribute so configuration binding can explicitly skip selected properties.

Changes

Added ConfigurationIgnoreAttribute to Microsoft.Extensions.Configuration.Abstractions (implementation + ref).
Reflection binder now skips ignored properties.
Constructor-parameter/property matching now treats ignored properties as non-bindable.
Source generator updated to parse and honor ignored properties.
Added tests for ignore behavior, ErrorOnUnknownConfiguration, and constructor matching with ignored properties.
Updated Abstractions README/PACKAGE examples.

Validation

dotnet build for Abstractions and Binder.
Binder unit tests: 296 passed, 0 failed.
Source-generation tests: 347 total, 0 failed (28 skipped by conditions).

dotnet-policy-service · 2026-04-01T06:26:34Z

Tagging subscribers to this area: @dotnet/area-extensions-configuration
See info in area-owners.md if you want to be subscribed.

Copilot

Pull request overview

Adds a new ConfigurationIgnoreAttribute to the configuration abstractions and updates both the reflection-based binder and the source generator so selected properties can be explicitly excluded from binding.

Changes:

Introduces ConfigurationIgnoreAttribute in Microsoft.Extensions.Configuration.Abstractions (impl + ref surface).
Updates reflection binder and source generator to skip ignored properties during binding and constructor-parameter matching.
Adds/extends tests and updates package documentation examples to cover ignore behavior and ErrorOnUnknownConfiguration.

Reviewed changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
src/libraries/Microsoft.Extensions.Configuration.Binder/tests/Common/ConfigurationBinderTests.TestClasses.cs	Adds a primary-ctor test type with an ignored property to validate ctor/property matching behavior.
src/libraries/Microsoft.Extensions.Configuration.Binder/tests/Common/ConfigurationBinderTests.Helpers.cs	Extends `ComplexOptions` with an ignored property for binder test coverage.
src/libraries/Microsoft.Extensions.Configuration.Binder/tests/Common/ConfigurationBinderTests.cs	Adds tests asserting ignored properties aren’t bound and don’t trip `ErrorOnUnknownConfiguration`, plus ctor-matching behavior.
src/libraries/Microsoft.Extensions.Configuration.Binder/src/ConfigurationBinder.cs	Skips ignored properties in reflection binding and in ctor-parameter/property equivalence checks; adds `IsIgnoredProperty`.
src/libraries/Microsoft.Extensions.Configuration.Binder/gen/Specs/TypeIndex.cs	Ensures generator considers `property.IsIgnored` when deciding if a property is bindable.
src/libraries/Microsoft.Extensions.Configuration.Binder/gen/Specs/Members/PropertySpec.cs	Adds `IsIgnored` flag to property spec model used by the generator.
src/libraries/Microsoft.Extensions.Configuration.Binder/gen/Parser/KnownTypeSymbols.cs	Adds symbol lookup for `ConfigurationIgnoreAttribute` for generator parsing.
src/libraries/Microsoft.Extensions.Configuration.Binder/gen/ConfigurationBindingGenerator.Parser.cs	Parses `[ConfigurationIgnore]` and attempts to incorporate it into property/ctor matching.
src/libraries/Microsoft.Extensions.Configuration.Abstractions/src/PACKAGE.md	Updates package example to mention/use `[ConfigurationIgnore]`.
src/libraries/Microsoft.Extensions.Configuration.Abstractions/src/ConfigurationIgnoreAttribute.cs	Adds the new public attribute type.
src/libraries/Microsoft.Extensions.Configuration.Abstractions/ref/Microsoft.Extensions.Configuration.Abstractions.cs	Adds the attribute to the reference assembly surface area.
src/libraries/Microsoft.Extensions.Configuration.Abstractions/README.md	Updates README example to mention/use `[ConfigurationIgnore]`.

Copilot · 2026-04-01T06:29:27Z

src/libraries/Microsoft.Extensions.Configuration.Abstractions/src/PACKAGE.md

 var dic = new Dictionary<string, string>
 {
    {"named_property", "value for named property"},
+    {"ignored_property", "this value is ignored"},


The sample uses the config key "ignored_property", which does not match the property name "IgnoredProperty" (and there's no ConfigurationKeyNameAttribute mapping). As a result, the example would keep the default value even without [ConfigurationIgnore], so it doesn’t actually demonstrate the ignore behavior. Consider using the matching key (e.g., "IgnoredProperty") or adding a ConfigurationKeyName mapping so the key would otherwise bind.

Suggested change

{"ignored_property", "this value is ignored"},

{"IgnoredProperty", "this value is ignored"},

Copilot · 2026-04-01T06:29:28Z

src/libraries/Microsoft.Extensions.Configuration.Abstractions/README.md

 var dic = new Dictionary<string, string>
 {
    {"named_property", "value for named property"},
+    {"ignored_property", "this value is ignored"},


Same issue as PACKAGE.md: the example sets "ignored_property" in configuration, but the property name is "IgnoredProperty" and no key-name mapping is provided. The value would remain "default" even without [ConfigurationIgnore], so the snippet doesn’t prove the attribute works. Prefer using a matching key ("IgnoredProperty") or add a ConfigurationKeyName mapping for the ignored property.

Suggested change

{"ignored_property", "this value is ignored"},

{"IgnoredProperty", "this value is ignored"},

Copilot · 2026-04-01T06:29:28Z

...raries/Microsoft.Extensions.Configuration.Binder/gen/ConfigurationBindingGenerator.Parser.cs

                        string parameterName = parameter.Name;

                        if (properties?.TryGetValue(parameterName, out PropertySpec? propertySpec) is not true)
                        {
                            (missingParameters ??= new()).Add(parameterName);
                        }
-                        else if (parameter.RefKind is not RefKind.None)
+                        else if (parameter.RefKind is not RefKind.None || propertySpec.IsIgnored)
                        {
                            (invalidParameters ??= new()).Add(parameterName);
                        }


Ctor-parameter matching treats an ignored property as an invalid parameter (leading to the CannotBindToConstructorParameter error), but the reflection binder treats ignored properties as non-bindable and fails with ConstructorParametersDoNotMatchProperties. To keep source-generated binding behavior/error messages consistent with the reflection binder, consider treating propertySpec.IsIgnored as if the property were missing (i.e., add to missingParameters instead of invalidParameters).

Copilot · 2026-04-01T06:29:28Z

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

        }

+        [Fact]
+        public void CanIgnoreConfigurationAttributes()


Test name is a bit ambiguous: this test is specifically validating [ConfigurationIgnore] behavior, but the name reads like it covers multiple attributes. Consider renaming to something more specific (e.g., CanIgnoreConfigurationIgnoreAttribute).

Suggested change

public void CanIgnoreConfigurationAttributes()

public void CanIgnoreConfigurationIgnoreAttribute()

Copilot · 2026-04-01T06:29:28Z

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

        }

+        [Fact]
+        public void ThrowOnClassWithPrimaryCtorAndIgnoredProperty()


For consistency with other test naming in this file (e.g., DoesNotThrowWhen...), consider using a verb form like "Throws..." / "ThrowsWhen..." rather than "ThrowOn...".

Suggested change

public void ThrowOnClassWithPrimaryCtorAndIgnoredProperty()

public void ThrowsOnClassWithPrimaryCtorAndIgnoredProperty()

tarekgh · 2026-04-01T16:44:51Z

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

            return propertyBindingPoint.Value;
        }

+        private static bool IsIgnoredProperty(PropertyInfo property)


This can be simplified as:

private static bool IsIgnoredProperty(PropertyInfo property) => property.IsDefined(typeof(ConfigurationIgnoreAttribute));

tarekgh · 2026-04-01T16:57:35Z

src/libraries/Microsoft.Extensions.Configuration.Binder/gen/Specs/TypeIndex.cs

        {
            TypeSpec propTypeSpec = GetEffectiveTypeSpec(property.TypeRef);
-            return IsAccessible() && !IsCollectionAndCannotOverride() && !IsDictWithUnsupportedKey();
+            return IsAccessible() && !property.IsIgnored && !IsCollectionAndCannotOverride() && !IsDictWithUnsupportedKey();


What happen when having a property with the ignore attribute and the configuration contains a matching key to this property? I guess in this case we can end-up with ErrorOnUnknownConfiguration. This will be inconsistent with the runtime binder too even with the changes here because GetAllProperties() which returns all properties (including ignored ones). It is worth adding a test case for that too.

rosebyte added 2 commits March 31, 2026 19:26

draft

1152bd2

cover constructor flows

142f4d8

Copilot AI review requested due to automatic review settings April 1, 2026 06:25

github-actions bot added the area-Extensions-Configuration label Apr 1, 2026

dotnet-policy-service bot assigned rosebyte Apr 1, 2026

Copilot started reviewing on behalf of rosebyte April 1, 2026 06:26 View session

Copilot AI reviewed Apr 1, 2026

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tarekgh added this to the 11.0.0 milestone Apr 1, 2026

tarekgh reviewed Apr 1, 2026

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Add COnfigurationIgnoreAttribute#126396

Add COnfigurationIgnoreAttribute#126396
rosebyte wants to merge 2 commits intodotnet:mainfrom
rosebyte:feature/configuration-ignore-attribute

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	{"ignored_property", "this value is ignored"},
	{"IgnoredProperty", "this value is ignored"},

	public void CanIgnoreConfigurationAttributes()
	public void CanIgnoreConfigurationIgnoreAttribute()

	public void ThrowOnClassWithPrimaryCtorAndIgnoredProperty()
	public void ThrowsOnClassWithPrimaryCtorAndIgnoredProperty()

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rosebyte commented Apr 1, 2026

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