Further fix to configuration classes using ISet, resolving regression with custom 404 pages

[AndyButland]

Prerequisites

• I have added steps to test this contribution in the description below

Resolves: #19567

Description

The cause of this issue was another cases of issues involved in the fix #19229, where ISet in configuration classes aren't bound.

Note that I've added a compatibility suppression for the breaking change, which I don't see how we can otherwise avoid.

Testing

Prepare a custom 404 page as per the instructions in the documentation (though note that I found this didn't work when using the name "404" for the document type and template, and instead used "File Not Found"). With this PR in place, the custom 404 should be displayed as expected.

To check via debugging, put a breaking point at the start of NotFoundHandlerHelper.GetCurrentNotFoundPageId and verify the error404Collection parameter matches the configured value.

Release

Can consider for a 16.0.1, otherwise 16.1.0.

[Copilot]

Pull Request Overview

This PR fixes the binding regression for custom 404 pages by changing the configuration property type and updating affected tests, and suppresses a compatibility warning.

• Changed Error404Collection from ISet<ContentErrorPage> to IEnumerable<ContentErrorPage> with a C# 12 collection expression default.
• Updated unit test initializer syntax in ContentSettingsValidatorTests.cs to use [...].
• Added a compatibility suppression for the breaking change in CompatibilitySuppressions.xml.

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
tests/Umbraco.Tests.UnitTests/Umbraco.Core/Configuration/Models/Validation/ContentSettingsValidatorTests.cs	Switched collection initializer syntax to C# 12 [...]
src/Umbraco.Core/Configuration/Models/ContentSettings.cs	Changed property type from ISet to IEnumerable
src/Umbraco.Core/CompatibilitySuppressions.xml	Added suppression for CP0002 on Error404Collection

Comments suppressed due to low confidence (2)

src/Umbraco.Core/Configuration/Models/ContentSettings.cs:53

• Changing Error404Collection from ISet to IEnumerable removes set semantics and mutability; consider using IReadOnlySet or IReadOnlyCollection to preserve uniqueness and clearly express intended behavior.

public IEnumerable<ContentErrorPage> Error404Collection { get; set; } = [];

src/Umbraco.Core/Configuration/Models/ContentSettings.cs:50

• [nitpick] The XML doc still implies set behavior; update the summary to reflect the change to an IEnumerable and clarify whether duplicates are permitted.

///     Gets or sets a value for the collection of error pages.

[henryson]

Will this also apply to version 15? I have the same problem in 15.4.1

[AndyButland]

Will this also apply to version 15? I have the same problem in 15.4.1

No, this is specifically fixing a regression issue in 16, so if you are having issues with 15 it'll likely be unrelated.

[kjac]

Looks good to me!

Please note that this is a breaking change due to the change of public signature. It is, however, a strictly necessary change which fixes a regression, and thus I'm accepting it for 16.1 👍

I also went the code route to test this 🤓

Given this code:

using Microsoft.Extensions.Options;
using Umbraco.Cms.Core.Composing;
using Umbraco.Cms.Core.Configuration.Models;

namespace Umbraco.Cms.Web.UI.Custom;

public class TestError404CollectionComponent : IComponent
{
    private readonly ContentSettings _contentSettings;
    private readonly ILogger<TestError404CollectionComponent> _logger;

    public TestError404CollectionComponent(
        IOptions<ContentSettings> contentSettings,
        ILogger<TestError404CollectionComponent> logger)
    {
        _logger = logger;
        _contentSettings = contentSettings.Value;
    }

    public void Initialize()
        => _logger.LogInformation(
            "### Found {numberOf404Configs} 404 page configs ###",
            // the fix is breaking, so this line needs updating after applying the fix
            _contentSettings.Error404Collection.Count);

    public void Terminate()
    {
    }
}

public class TestError404CollectionComposer : ComponentComposer<TestError404CollectionComponent>
{
}

...and this 404 configuration:

"Error404Collection": [
  {
	"Culture": "en-us",
	"ContentKey": "575b9a71-28d2-47b0-bd94-ab98e0fc5f2d"
  },
  {
	"Culture": "da-dk",
	"ContentKey": "d35282e3-3a2d-4566-965a-c2d91b0fe46e"
  }
]

Without the fix I get: ### Found 0 404 page configs ### ❌

With the fix I get the expected: ### Found 2 404 page configs ### ✅

[umbracocommunity]

This pull request has been mentioned on Umbraco community forum. There might be relevant details there:

https://forum.umbraco.com/t/issue-with-404-page-configuration/4471/5

[thenexus00]

I do not believe this is fixed with any default behavior.
In two 16.1.1 builds nothing I have tried works.

• I followed the documentation to the letter - does not work.
• I just had a different document type page - does not work
• I tried moving the custom 404 page across multiple locations - does not work
• I have tried in appsettings the ContentKey, I tried the old ContentId as well both with GUID and old style ID which did not work. I tried content X Path as well in both URL and name - did not work.
• I removed all I could from program.cs so it was bare and just loaded the site and that still did not work.
• I tried my own custom middleware - still did not work.

I am about to try the code kjac l posted but if that is the only thing that works I do not consider this a working solution.

[thenexus00]

I do not believe this is fixed with any default behavior. In two 16.1.1 builds nothing I have tried works.

• I followed the documentation to the letter - does not work.
• I just had a different document type page - does not work
• I tried moving the custom 404 page across multiple locations - does not work
• I have tried in appsettings the ContentKey, I tried the old ContentId as well both with GUID and old style ID which did not work. I tried content X Path as well in both URL and name - did not work.
• I removed all I could from program.cs so it was bare and just loaded the site and that still did not work.
• I tried my own custom middleware - still did not work.

I am about to try the code kjac l posted but if that is the only thing that works I do not consider this a working solution.

I have only been able to solve the issue with custom middleware targeting
context.Response.StatusCode == 404