DependencyInjection generic constraint validation incorrectly rejects struct constraint on mobile #127564

Reasoning

Microsoft.Extensions.DependencyInjection.Tests is failing on mobile platforms (iOS, tvOS, macCatalyst, Android) with errors related to generic constraint validation. The DI container's ValidateTrimmingAnnotations method is incorrectly rejecting implementations that have a new() constraint when the service interface doesn't have one.

The error states:

Generic implementation type 'ClassWithStructConstraint1' has a DefaultConstructorConstraint ('new()' constraint), but the generic service type 'IFakeOpenGenericService1' doesn't.

This validation is overly restrictive. An implementation can have more constraints than the interface it implements — that's valid and safe. The constraint on the implementation guarantees that any type argument passed will satisfy the implementation's needs, which includes satisfying the less-restrictive interface. The validation logic appears to be requiring exact constraint matching instead of allowing implementation constraints to be a superset of interface constraints.

This is a product bug in the DI container's constraint validation logic, not a test issue. The same tests pass on desktop platforms.

Impact on platforms

Failing on all tested mobile platforms in build 1399212 (2026-04-28):

• maccatalyst-arm64 / OSX.15.Arm64.Open / exit code 1
• iossimulator-arm64 / OSX.15.Arm64.Open / exit code 1
• iossimulator-x64 / OSX.15.Amd64.Open / exit code 1
• tvos-arm64 / osx.15.amd64.appletv.open / exit code 1
• android (multiple architectures) / Windows.11.Amd64.Android.Open / exit code 1

Errors log

From maccatalyst-arm64 Helix work item Microsoft.Extensions.DependencyInjection.Tests (console log):

1) 	[FAIL] Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteFactoryTest.CreateCallSite_ReturnsService_IfClosedTypeSatisfiesStructGenericConstraint
   Assembly:  [Microsoft.Extensions.DependencyInjection.Tests, Version=11.0.0.0, Culture=neutral, PublicKeyToken=adb9793829ddae60]
   Exception messages: System.ArgumentException : Generic implementation type 'Microsoft.Extensions.DependencyInjection.Specification.Fakes.ClassWithStructConstraint`1' has a DefaultConstructorConstraint ('new()' constraint), but the generic service type 'Microsoft.Extensions.DependencyInjection.Specification.Fakes.IFakeOpenGenericService`1' doesn't.
   Exception stack traces:    at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteFactory.ValidateTrimmingAnnotations(Type serviceType, Type[] serviceTypeGenericArguments, Type implementationType, Type[] implementationTypeGenericArguments)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteFactory.Populate()
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteFactoryTest.GetCallSiteFactory(ServiceDescriptor[] descriptors)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteFactoryTest.CreateCallSite_ReturnsService_IfClosedTypeSatisfiesStructGenericConstraint()
   at System.Reflection.MethodBaseInvoker.InterpretedInvoke_Method(Object obj, IntPtr* args)
   at System.Reflection.MethodBaseInvoker.InvokeWithNoArgs(Object obj, BindingFlags invokeAttr)

2) 	[FAIL] Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteFactoryTest.CreateCallSite_Throws_IfClosedTypeDoesNotSatisfyStructGenericConstraint
   Exception messages: System.ArgumentException : Generic implementation type 'Microsoft.Extensions.DependencyInjection.Specification.Fakes.ClassWithNewConstraint`1' has a DefaultConstructorConstraint ('new()' constraint), but the generic service type 'Microsoft.Extensions.DependencyInjection.Specification.Fakes.IFakeOpenGenericService`1' doesn't.

3) 	[FAIL] Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteFactoryTest.CreateCallSite_Throws_IfClosedTypeDoesNotSatisfyNewGenericConstraint
   Exception messages: System.ArgumentException : Generic implementation type 'Microsoft.Extensions.DependencyInjection.Specification.Fakes.ClassWithStructConstraint`1' has a DefaultConstructorConstraint ('new()' constraint), but the generic service type 'Microsoft.Extensions.DependencyInjection.Specification.Fakes.IFakeOpenGenericService`1' doesn't.

4) 	[FAIL] Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteFactoryTest.CreateCallSite_ReturnsService_IfClosedTypeSatisfiesNewGenericConstraint
   Exception messages: System.ArgumentException : Generic implementation type 'Microsoft.Extensions.DependencyInjection.Specification.Fakes.ClassWithNewConstraint`1' has a DefaultConstructorConstraint ('new()' constraint), but the generic service type 'Microsoft.Extensions.DependencyInjection.Specification.Fakes.IFakeOpenGenericService`1' doesn't.

First build it occurred

First observed (within the scanned window) in build 1399212, which finished on 2026-04-28T07:31:50Z (commit 2ac6372).

Note: This window represents the last ~8 days of builds. The true origin may be earlier.

Occurrences in scanned window: Present in mobile library test jobs in the most recent build (multiple test failures in the same assembly).

Recommended action

1. Area owner: @dotnet/area-extensions-dependencyinjection should investigate why ValidateTrimmingAnnotations in CallSiteFactory is rejecting valid constraint combinations on mobile platforms.

2. Root cause: The validation logic at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteFactory.ValidateTrimmingAnnotations appears to be enforcing exact constraint matching between service interface and implementation type. This is incorrect — implementations are allowed to have stricter (more specific) constraints than their interfaces.

   For example, if IService<T> has no constraints and Service<T> : IService<T> where T : struct, new(), this should be valid. The implementation's constraints are a subset of valid type arguments, which is safe.

3. Investigation steps:

   • Locate ValidateTrimmingAnnotations in src/libraries/Microsoft.Extensions.DependencyInjection/src/ServiceLookup/CallSiteFactory.cs
   • Check if the validation logic differs on mobile platforms (e.g., due to platform-specific compilation symbols or trimming mode)
   • Review recent changes to the constraint validation logic
   • Verify that desktop platforms don't hit this validation (or that they skip it via a different code path)

4. Expected fix: Update ValidateTrimmingAnnotations to allow implementation types to have constraints that are a superset (more restrictive) of the service type's constraints. The validation should only fail when the implementation's constraints are less restrictive than required by the service interface.

tools:
  github:
    min-integrity: approved  # merged | approved | unapproved | none

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