Bugfix: hide Self link in included resources for missing controller

src/JsonApiDotNetCore/Serialization/Response/LinkBuilder.cs

@@ -312,6 +312,13 @@ private bool ShouldIncludeResourceLink(LinkTypes linkType, ResourceType resource
 
     protected virtual string? RenderLinkForAction(string? controllerName, string actionName, IDictionary<string, object?> routeValues)
     {
+        if (controllerName == null)
+        {
+            // When passing null to LinkGenerator, it uses the controller for the current endpoint. This is incorrect for
+            // included resources of a different resource type: it should hide its links when there's no controller for them.
+            return null;
+        }
+
         return _options.UseRelativeLinks
             ? _linkGenerator.GetPathByAction(HttpContext, actionName, controllerName, routeValues)
             : _linkGenerator.GetUriByAction(HttpContext, actionName, controllerName, routeValues);

test/JsonApiDotNetCoreTests/IntegrationTests/Links/LinkInclusionIncludeTests.cs

@@ -0,0 +1,65 @@
+using System.Net;
+using FluentAssertions;
+using JsonApiDotNetCore.Serialization.Objects;
+using TestBuildingBlocks;
+using Xunit;
+
+namespace JsonApiDotNetCoreTests.IntegrationTests.Links;
+
+public sealed class LinkInclusionIncludeTests : IClassFixture<IntegrationTestContext<TestableStartup<LinksDbContext>, LinksDbContext>>
+{
+    private readonly IntegrationTestContext<TestableStartup<LinksDbContext>, LinksDbContext> _testContext;
+    private readonly LinksFakers _fakers = new();
+
+    public LinkInclusionIncludeTests(IntegrationTestContext<TestableStartup<LinksDbContext>, LinksDbContext> testContext)
+    {
+        _testContext = testContext;
+
+        testContext.UseController<PhotoLocationsController>();
+    }
+
+    [Fact]
+    public async Task Hides_links_for_unregistered_controllers()
+    {
+        // Arrange
+        PhotoLocation location = _fakers.PhotoLocation.Generate();
+        location.Photo = _fakers.Photo.Generate();
+        location.Album = _fakers.PhotoAlbum.Generate();
+
+        await _testContext.RunOnDatabaseAsync(async dbContext =>
+        {
+            dbContext.PhotoLocations.Add(location);
+            await dbContext.SaveChangesAsync();
+        });
+
+        string route = $"/photoLocations/{location.StringId}?include=photo,album";
+
+        // Act
+        (HttpResponseMessage httpResponse, Document responseDocument) = await _testContext.ExecuteGetAsync<Document>(route);
+
+        // Assert
+        httpResponse.Should().HaveStatusCode(HttpStatusCode.OK);
+
+        responseDocument.Data.SingleValue.ShouldNotBeNull();
+
+        responseDocument.Data.SingleValue.Relationships.ShouldContainKey("photo").With(value =>
+        {
+            value.ShouldNotBeNull();
+            value.Links.ShouldNotBeNull();
+        });
+
+        responseDocument.Included.ShouldHaveCount(2);
+
+        responseDocument.Included.Should().ContainSingle(resource => resource.Type == "photos").Subject.With(resource =>
+        {
+            resource.Links.Should().BeNull();
+            resource.Relationships.Should().BeNull();
+        });
+
+        responseDocument.Included.Should().ContainSingle(resource => resource.Type == "photoAlbums").Subject.With(resource =>
+        {
+            resource.Links.Should().BeNull();
+            resource.Relationships.Should().BeNull();
+        });
+    }
+}

test/JsonApiDotNetCoreTests/IntegrationTests/Links/LinkInclusionTests.cs

@@ -17,6 +17,7 @@ public LinkInclusionTests(IntegrationTestContext<TestableStartup<LinksDbContext>
 
         testContext.UseController<PhotosController>();
         testContext.UseController<PhotoLocationsController>();
+        testContext.UseController<PhotoAlbumsController>();
     }
 
     [Fact]

test/JsonApiDotNetCoreTests/IntegrationTests/ReadWrite/Creating/CreateResourceWithToOneRelationshipTests.cs

@@ -22,6 +22,7 @@ public CreateResourceWithToOneRelationshipTests(IntegrationTestContext<TestableS
         testContext.UseController<WorkItemGroupsController>();
         testContext.UseController<WorkItemsController>();
         testContext.UseController<RgbColorsController>();
+        testContext.UseController<UserAccountsController>();
 
         var options = (JsonApiOptions)testContext.Factory.Services.GetRequiredService<IJsonApiOptions>();
         options.AllowClientGeneratedIds = true;

test/JsonApiDotNetCoreTests/IntegrationTests/ReadWrite/Fetching/FetchResourceTests.cs

@@ -17,6 +17,7 @@ public FetchResourceTests(IntegrationTestContext<TestableStartup<ReadWriteDbCont
 
         testContext.UseController<WorkItemsController>();
         testContext.UseController<UserAccountsController>();
+        testContext.UseController<WorkTagsController>();
     }
 
     [Fact]

test/JsonApiDotNetCoreTests/IntegrationTests/ReadWrite/Updating/Resources/ReplaceToManyRelationshipTests.cs

@@ -19,6 +19,7 @@ public ReplaceToManyRelationshipTests(IntegrationTestContext<TestableStartup<Rea
         _testContext = testContext;
 
         testContext.UseController<WorkItemsController>();
+        testContext.UseController<UserAccountsController>();
 
         testContext.ConfigureServicesAfterStartup(services =>
         {

test/JsonApiDotNetCoreTests/IntegrationTests/ReadWrite/Updating/Resources/UpdateToOneRelationshipTests.cs

@@ -20,6 +20,7 @@ public UpdateToOneRelationshipTests(IntegrationTestContext<TestableStartup<ReadW
         testContext.UseController<WorkItemsController>();
         testContext.UseController<WorkItemGroupsController>();
         testContext.UseController<RgbColorsController>();
+        testContext.UseController<UserAccountsController>();
 
         testContext.ConfigureServicesAfterStartup(services =>
         {

test/JsonApiDotNetCoreTests/IntegrationTests/ReadWrite/WorkTag.cs

@@ -5,6 +5,7 @@
 namespace JsonApiDotNetCoreTests.IntegrationTests.ReadWrite;
 
 [UsedImplicitly(ImplicitUseTargetFlags.Members)]
+[Resource(ControllerNamespace = "JsonApiDotNetCoreTests.IntegrationTests.ReadWrite")]
 public sealed class WorkTag : Identifiable<int>
 {
     [Attr]

test/JsonApiDotNetCoreTests/UnitTests/Links/LinkInclusionTests.cs

@@ -1,4 +1,5 @@
 using FluentAssertions;
+using Humanizer;
 using JsonApiDotNetCore.Configuration;
 using JsonApiDotNetCore.Middleware;
 using JsonApiDotNetCore.Queries;
@@ -68,7 +69,10 @@ public void Applies_cascading_settings_for_top_level_links(LinkTypes linksInReso
             PrimaryId = "1",
             IsCollection = true,
             Kind = EndpointKind.Relationship,
-            Relationship = new HasOneAttribute()
+            Relationship = new HasOneAttribute
+            {
+                LeftType = exampleResourceType
+            }
         };
 
         var paginationContext = new PaginationContext
@@ -386,7 +390,7 @@ public ResourceType GetResourceTypeForController(Type? controllerType)
 
         public string? GetControllerNameForResourceType(ResourceType? resourceType)
         {
-            return null;
+            return resourceType == null ? null : $"{resourceType.PublicName.Pascalize()}Controller";
         }
     }