Preserve existing Examine FieldDefinitionCollection if it already exists

[callumbwhyte]

As discussed on #20267 v16 introduced a behavioural breaking change whereby Umbraco's own Examine index configuration now happens at an undetermined point in the startup lifecycle, compared with previously running as part of the core Umbraco boot steps.

This can cause issues when trying to customise the Examine index, e.g. setting field types, as you don't know whether your code is going to run before or after Umbraco's.

I explained a bit more about how this came to be here:

This was caused by #18988 - where the registration of Examine (and therefore Umbraco's own configuration of LuceneDirectoryIndexOptions) was moved from happening inside builder.AddBackOffice() to a composer. This meant it went from being (almost) guaranteed to run first, as AddBackOffice is called first from Program.cs, to an unknown order.

Other than the [ComposeBefore] / [ComposeAfter] attributes I can't see a way of forcing Umbraco's Examine composer to run before any user registered ones...

The solution is of course to add decorate your IComposer with [ComposeAfter(typeof(AddExamineComposer))] as per the docs - but this has been problematic for me in my Search Extensions package where I am multi-targeting 🙈 and can't reliably target this change to V16+ as V15 also uses .NET 9 where AddExamineComposer does not exist...

After digging into things I found the real issue is Umbraco assumes it's okay to set the FieldDefinitions property during configuration, without consideration for if this has already been set. The fix is simple: when Umbraco's configuration code runs, ensure any existing config is applied too. I have added an overload to UmbracoFieldDefinitionCollection that takes an existing FieldDefinitionCollection and tries to add each existing definition to the UmbracoFieldDefinitionCollection. Examine sets this property to an empty collection on initialisation (here) anyway so it should always be set.

I believe it would be good to get this fix into both V16 and V17 to prevent confusion as others have been experiencing!

[github-actions]

Hi there @callumbwhyte, thank you for this contribution! 👍

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[Copilot]

Pull request overview

This pull request adds functionality to preserve existing field definitions when configuring Umbraco Examine indexes. Previously, the ConfigureIndexOptions class would always create a new UmbracoFieldDefinitionCollection from scratch, which would discard any custom field definitions that may have been registered by extension code before the configuration runs.

Key Changes:

• Added a new constructor to UmbracoFieldDefinitionCollection that accepts an existing FieldDefinitionCollection and merges its definitions with the base Umbraco field definitions
• Updated ConfigureIndexOptions to use the new constructor, passing the existing options.FieldDefinitions to preserve any pre-existing customizations

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
src/Umbraco.Infrastructure/Examine/UmbracoFieldDefinitionCollection.cs	Adds a new constructor that accepts and merges existing field definitions
src/Umbraco.Examine.Lucene/DependencyInjection/ConfigureIndexOptions.cs	Updates all three index configurations (Internal, External, Members) to preserve existing field definitions using the new constructor

[Copilot]

The new constructor does not handle the case where definitions parameter is null. If options.FieldDefinitions is null when this constructor is called (from ConfigureIndexOptions.cs), it will throw a NullReferenceException when trying to iterate. Consider adding a null check:

public UmbracoFieldDefinitionCollection(FieldDefinitionCollection? definitions)
    : base(UmbracoIndexFieldDefinitions)
{
    if (definitions != null)
    {
        foreach (var definition in definitions)
        {
            AddOrUpdate(definition);
        }
    }
}

Suggested change

	foreach (var definition in definitions)
	{
	AddOrUpdate(definition);
	if (definitions != null)
	{
	foreach (var definition in definitions)
	{
	AddOrUpdate(definition);
	}