fix: honor InternalsVisibleTo when checking constructor accessibility

Source/Awaiten.SourceGenerators/AwaitenGenerator.Classification.cs

@@ -188,12 +188,14 @@ private static void ReportWhenUnregistered(ParameterModel parameterModel, ImplIn
 
 	/// <summary>
 	///     The container-wide inputs an injected-member classification reads, bundled so the classification methods
-	///     stay small: the container symbol, the coalesced service map, the constraint-rejected and consumed-context
-	///     sets, the <c>[ImportService&lt;T&gt;]</c> external service types (a member of one resolves externally
-	///     rather than being reported missing), and the diagnostics sink.
+	///     stay small: the container symbol, the compilation (which answers whether a setter is reachable from the
+	///     container), the coalesced service map, the constraint-rejected and consumed-context sets, the
+	///     <c>[ImportService&lt;T&gt;]</c> external service types (a member of one resolves externally rather than
+	///     being reported missing), and the diagnostics sink.
 	/// </summary>
 	private sealed record InjectionContext(
 		INamedTypeSymbol ContainerSymbol,
+		Compilation Compilation,
 		Dictionary<ServiceKey, string> ServiceToImpl,
 		HashSet<string> ConstraintRejected,
 		HashSet<ServiceKey> ConsumedConditionals,
@@ -341,11 +343,12 @@ private static IEnumerable<IPropertySymbol> InjectedProperties(INamedTypeSymbol
 		LocationInfo? location = spec.EntryLocation ?? LocationInfo.From(property.Locations.FirstOrDefault());
 
 		// AWT136: an injected property must have a set/init accessor the container can assign through the object
-		// initializer. The container is not a derived type, so a protected/private-protected setter (and a
-		// cross-assembly internal one) is out of reach even though not private. Apply the same accessibility test
-		// the constructor path uses rather than a bare not-private check, so an unreachable setter surfaces as
-		// AWT136 instead of an inaccessible-setter error in generated code.
-		if (property.SetMethod is not { } setter || !IsAccessibleSetter(setter, context.ContainerSymbol))
+		// initializer. The container is not a derived type, so a protected/private-protected setter (and an
+		// internal one in an assembly that grants the container no [InternalsVisibleTo]) is out of reach even
+		// though not private. Apply the same accessibility test the constructor path uses rather than a bare
+		// not-private check, so an unreachable setter surfaces as AWT136 instead of an inaccessible-setter error
+		// in generated code.
+		if (property.SetMethod is not { } setter || !IsAccessibleSetter(setter, context.ContainerSymbol, context.Compilation))
 		{
 			context.Diagnostics.Add(new DiagnosticInfo(
 				Diagnostics.InjectedPropertyNotSettable,
@@ -496,17 +499,12 @@ private static bool RejectsInjectedPropertyShape(
 		return false;
 	}
 
-	// The setter must be reachable from the container's object initializer, which is not a derived context.
-	// Mirrors IsAccessibleConstructor: public always, internal/protected-internal only within the container's own
-	// assembly, and protected/private-protected/private never (the container cannot reach them).
-	private static bool IsAccessibleSetter(IMethodSymbol setter, INamedTypeSymbol containerSymbol)
-		=> setter.DeclaredAccessibility switch
-		{
-			Accessibility.Public => true,
-			Accessibility.Internal or Accessibility.ProtectedOrInternal =>
-				SymbolEqualityComparer.Default.Equals(setter.ContainingAssembly, containerSymbol.ContainingAssembly),
-			_ => false,
-		};
+	// The setter must be reachable from the container's object initializer. Asks Roslyn the same way constructor
+	// selection does (see SelectConstructor), so the two agree: public always, internal/protected-internal within
+	// the container's own assembly or across an [InternalsVisibleTo] boundary, and protected/private-protected/
+	// private never, since the container neither derives from the implementation nor sits inside it.
+	private static bool IsAccessibleSetter(IMethodSymbol setter, INamedTypeSymbol containerSymbol, Compilation compilation)
+		=> compilation.IsSymbolAccessibleWithin(setter, containerSymbol);
 
 	/// <summary>
 	///     Classifies a constructor parameter as a runtime argument (<c>[Arg]</c>), a deferred relationship type

Source/Awaiten.SourceGenerators/AwaitenGenerator.Collection.cs

@@ -45,7 +45,7 @@ private static (List<RawRegistration> Raw, HashSet<string> ConstraintRejectedSer
 		// implementation (iterating to a fixpoint over its own generic dependencies).
 		if (open.Count > 0)
 		{
-			ExpandOpenGenerics(result, open, containerSymbol, external, diagnostics, constraintRejected);
+			ExpandOpenGenerics(result, open, containerSymbol, compilation, external, diagnostics, constraintRejected);
 		}
 
 		// ...then moved back to the end: coalescing is first-wins per service, so the explicit registrations and

Source/Awaiten.SourceGenerators/AwaitenGenerator.Decorators.cs

@@ -321,7 +321,7 @@ private readonly record struct ServiceChain(
 		/// </summary>
 		private string? SingleInnerParameterType(INamedTypeSymbol decorator, INamedTypeSymbol service)
 		{
-			IMethodSymbol? constructor = SelectConstructor(decorator, _containerSymbol, _serviceToImpl.Keys.Select(k => k.Service), _external);
+			IMethodSymbol? constructor = SelectConstructor(decorator, _containerSymbol, _compilation, _serviceToImpl.Keys.Select(k => k.Service), _external);
 			if (constructor is null)
 			{
 				return null;
@@ -612,7 +612,7 @@ private static CompositeCollectionKind ClassifyCompositeCollection(
 		out string? relatedElement)
 	{
 		relatedElement = null;
-		IMethodSymbol? constructor = SelectConstructor(composite, containerSymbol, serviceToImpl.Keys.Select(k => k.Service), external);
+		IMethodSymbol? constructor = SelectConstructor(composite, containerSymbol, compilation, serviceToImpl.Keys.Select(k => k.Service), external);
 		if (constructor is null)
 		{
 			return CompositeCollectionKind.Missing;

Source/Awaiten.SourceGenerators/AwaitenGenerator.OpenGenerics.cs

@@ -190,6 +190,7 @@ private static void ExpandOpenGenerics(
 		List<RawRegistration> raw,
 		List<OpenRegistration> open,
 		INamedTypeSymbol containerSymbol,
+		Compilation compilation,
 		ExternalSurface external,
 		List<DiagnosticInfo> diagnostics,
 		HashSet<string> constraintRejected)
@@ -247,7 +248,7 @@ private static void ExpandOpenGenerics(
 				continue;
 			}
 
-			foreach (ITypeSymbol required in RequiredServiceTypes(impl, containerSymbol, raw, openServices, external))
+			foreach (ITypeSymbol required in RequiredServiceTypes(impl, containerSymbol, compilation, raw, openServices, external))
 			{
 				if (required is INamedTypeSymbol { IsGenericType: true, IsUnboundGenericType: false, } closed
 				    && expandedServices.Add(closed.ToDisplayString(FullyQualified)))
@@ -379,13 +380,15 @@ private static void ReportExpansionTooDeep(INamedTypeSymbol impl, int depth, Exp
 	private static IEnumerable<ITypeSymbol> RequiredServiceTypes(
 		INamedTypeSymbol implementation,
 		INamedTypeSymbol containerSymbol,
+		Compilation compilation,
 		List<RawRegistration> raw,
 		HashSet<INamedTypeSymbol> openServices,
 		ExternalSurface external)
 	{
 		IMethodSymbol? constructor = AwaitenGenerator.SelectConstructor(
 			implementation,
 			containerSymbol,
+			compilation,
 			raw.Select(r => r.ServiceType),
 			external,
 			p => IsOpenGenericSatisfiable(p.Type, openServices));

Source/Awaiten.SourceGenerators/AwaitenGenerator.Production.cs

@@ -172,7 +172,7 @@ private static List<MemberModel> BuildInjectedMembers(ImplInfo info, BuildContex
 
 		DiscoverInjectedMembers(
 			info,
-			new InjectionContext(context.ContainerSymbol, context.ServiceToImpl, context.ConstraintRejected, context.ConsumedConditionals, context.External.ServiceTypes, context.Diagnostics),
+			new InjectionContext(context.ContainerSymbol, context.Compilation, context.ServiceToImpl, context.ConstraintRejected, context.ConsumedConditionals, context.External.ServiceTypes, context.Diagnostics),
 			injectProperties,
 			members);
 		return members;
@@ -253,7 +253,7 @@ private static InstanceModel BuildPrebuiltInstance(
 			return null;
 		}
 
-		IMethodSymbol? constructor = SelectConstructor(info.Symbol, containerSymbol, serviceToImpl.Keys.Select(k => k.Service), external);
+		IMethodSymbol? constructor = SelectConstructor(info.Symbol, containerSymbol, compilation, serviceToImpl.Keys.Select(k => k.Service), external);
 		if (constructor is null)
 		{
 			diagnostics.Add(new DiagnosticInfo(
@@ -298,7 +298,7 @@ private static (string? Hook, EquatableArray<ParameterModel> Parameters) Resolve
 		Compilation compilation = context.Compilation;
 
 		List<IMethodSymbol> matches = new();
-		foreach (ISymbol member in AccessibleMembers(info.Origin ?? containerSymbol, hookName))
+		foreach (ISymbol member in AccessibleMembers(info.Origin ?? containerSymbol, hookName, compilation))
 		{
 			// A module hook must also be accessible from the generated container (its own private members are
 			// reachable from the partial, a module's are not); an inaccessible module method is not a usable hook.
@@ -591,7 +591,7 @@ private static void ValidateInstanceMember(
 		List<DiagnosticInfo> diagnostics)
 	{
 		bool inaccessibleMatch = false;
-		foreach (ISymbol member in AccessibleMembers(info.Origin ?? containerSymbol, info.ProductionMember!))
+		foreach (ISymbol member in AccessibleMembers(info.Origin ?? containerSymbol, info.ProductionMember!, compilation))
 		{
 			ITypeSymbol? memberType = member switch
 			{
@@ -666,12 +666,17 @@ private static string DescribeOwner(ImplInfo info)
 	internal static IMethodSymbol? SelectConstructor(
 		INamedTypeSymbol implementation,
 		INamedTypeSymbol containerSymbol,
+		Compilation compilation,
 		IEnumerable<string> registeredServices,
 		ExternalSurface external,
 		Func<IParameterSymbol, bool>? additionallySatisfiable = null)
 	{
+		// The generated partial emits the 'new' from inside the container, so what the container can reach is
+		// exactly Roslyn's own accessibility question, which honors [InternalsVisibleTo]. A bare same-assembly
+		// comparison would reject a referenced assembly's internal constructor the generated code could in fact
+		// call. The module member checks ask it the same way (see ResolveFactory).
 		List<IMethodSymbol> constructors = implementation.InstanceConstructors
-			.Where(c => IsAccessibleConstructor(c, containerSymbol))
+			.Where(c => compilation.IsSymbolAccessibleWithin(c, containerSymbol))
 			.ToList();
 		if (constructors.Count <= 1)
 		{
@@ -699,27 +704,16 @@ private static string DescribeOwner(ImplInfo info)
 
 		// Fall back to the greediest constructor so its unresolved parameters surface as AWT101.
 		return resolvable ?? constructors.OrderByDescending(c => c.Parameters.Length).First();
-
-		static bool IsAccessibleConstructor(IMethodSymbol constructor, INamedTypeSymbol containerSymbol)
-		{
-			return constructor.DeclaredAccessibility switch
-			{
-				Accessibility.Public => true,
-				Accessibility.Internal or Accessibility.ProtectedOrInternal =>
-					SymbolEqualityComparer.Default.Equals(
-						constructor.ContainingAssembly, containerSymbol.ContainingAssembly),
-				_ => false,
-			};
-		}
 	}
 
 	/// <summary>
 	///     The members named <paramref name="name" /> the generated container partial can reach: the
 	///     container's own members (any accessibility, since a partial can use its own private members) plus
-	///     inherited members a derived type can access (everything but private, with internal / private-protected
-	///     restricted to the same assembly).
+	///     inherited members the container can access, which is Roslyn's own check: a base type's protected member
+	///     qualifies (the container derives from it) and an internal one does when the declaring assembly is the
+	///     container's or grants it [InternalsVisibleTo].
 	/// </summary>
-	private static IEnumerable<ISymbol> AccessibleMembers(INamedTypeSymbol container, string name)
+	private static IEnumerable<ISymbol> AccessibleMembers(INamedTypeSymbol container, string name, Compilation compilation)
 	{
 		foreach (ISymbol member in container.GetMembers(name))
 		{
@@ -728,20 +722,11 @@ private static IEnumerable<ISymbol> AccessibleMembers(INamedTypeSymbol container
 
 		for (INamedTypeSymbol? baseType = container.BaseType; baseType is not null; baseType = baseType.BaseType)
 		{
-			foreach (ISymbol member in baseType.GetMembers(name).Where(m => IsAccessibleFromDerived(m, container)))
+			foreach (ISymbol member in baseType.GetMembers(name).Where(m => compilation.IsSymbolAccessibleWithin(m, container)))
 			{
 				yield return member;
 			}
 		}
-
-		static bool IsAccessibleFromDerived(ISymbol member, INamedTypeSymbol container)
-			=> member.DeclaredAccessibility switch
-			{
-				Accessibility.Public or Accessibility.Protected or Accessibility.ProtectedOrInternal => true,
-				Accessibility.Internal or Accessibility.ProtectedAndInternal =>
-					SymbolEqualityComparer.Default.Equals(member.ContainingAssembly, container.ContainingAssembly),
-				_ => false,
-			};
 	}
 
 	/// <summary>
@@ -756,7 +741,7 @@ private static List<IMethodSymbol> FindFactoryCandidates(
 		INamedTypeSymbol container, string name, ITypeSymbol serviceType, Compilation compilation)
 	{
 		List<IMethodSymbol> candidates = new();
-		foreach (ISymbol member in AccessibleMembers(container, name))
+		foreach (ISymbol member in AccessibleMembers(container, name, compilation))
 		{
 			if (member is IMethodSymbol { MethodKind: MethodKind.Ordinary, } method
 			    && compilation.HasImplicitConversion(ProducedType(method.ReturnType, compilation), serviceType))

Source/Awaiten.SourceGenerators/AwaitenGenerator.Scan.cs

@@ -1102,7 +1102,7 @@ private static bool PruneUnconstructableScanRound(
 		{
 			if (pinnedImpls.Contains(registration.ImplementationType)
 			    || !checkedImpls.Add(registration.ImplementationType)
-			    || FirstUnconstructableReason(registration.Implementation, containerSymbol, services, constraintRejected, external, variance) is not { } reason)
+			    || FirstUnconstructableReason(registration.Implementation, containerSymbol, compilation, services, constraintRejected, external, variance) is not { } reason)
 			{
 				continue;
 			}
@@ -1134,13 +1134,14 @@ private static bool PruneUnconstructableScanRound(
 	private static string? FirstUnconstructableReason(
 		INamedTypeSymbol implementation,
 		INamedTypeSymbol containerSymbol,
+		Compilation compilation,
 		HashSet<ServiceKey> services,
 		HashSet<string> constraintRejected,
 		ExternalSurface external,
 		VarianceState variance)
 	{
 		IMethodSymbol? constructor = SelectConstructor(
-			implementation, containerSymbol, services.Select(service => service.Service), external);
+			implementation, containerSymbol, compilation, services.Select(service => service.Service), external);
 		if (constructor is null)
 		{
 			return "it has no constructor accessible to the container";
@@ -1164,7 +1165,7 @@ model.Kind is DependencyKind.Arg or DependencyKind.External
 
 		foreach (IPropertySymbol property in InjectedProperties(implementation))
 		{
-			if (UnsatisfiableInjectedMemberReason(property, containerSymbol, services, constraintRejected, external.ServiceTypes) is { } reason)
+			if (UnsatisfiableInjectedMemberReason(property, containerSymbol, compilation, services, constraintRejected, external.ServiceTypes) is { } reason)
 			{
 				return reason;
 			}
@@ -1182,12 +1183,13 @@ model.Kind is DependencyKind.Arg or DependencyKind.External
 	private static string? UnsatisfiableInjectedMemberReason(
 		IPropertySymbol property,
 		INamedTypeSymbol containerSymbol,
+		Compilation compilation,
 		HashSet<ServiceKey> services,
 		HashSet<string> constraintRejected,
 		HashSet<string> externalServiceTypes)
 	{
 		ParameterModel member = ClassifyDependency(property.Type, property.GetAttributes(), asyncFactory: false, location: null, externalServiceTypes);
-		if (property.SetMethod is not { } setter || !IsAccessibleSetter(setter, containerSymbol)
+		if (property.SetMethod is not { } setter || !IsAccessibleSetter(setter, containerSymbol, compilation)
 		    || member.Kind is DependencyKind.Arg or DependencyKind.External || IsInjectOptional(property.GetAttributes()))
 		{
 			return null;