Options validation source generator doesn't consider constructing ValidationContext with an IServiceProvider

[jander-msft]

Using the following example source:

public interface IMyValidationService { }

public sealed class MyOptions : IValidatableObject
{
    public IEnumerable<ValidationResult> Validate(ValidationContext validationContext)
    {
        // This will throw since an IServiceProvider is not available in the ValidationContext
        _ = validationContext.GetRequiredService<IMyValidationService>();
        return [];
    }
}

[OptionsValidator]
public sealed partial class MyValidateOptions :
    IValidateOptions<MyOptions>
{
}

would generate an options validation implementation that looks like:

partial class MyValidateOptions
{
    /// <summary>
    /// Validates a specific named options instance (or all when <paramref name="name"/> is <see langword="null" />).
    /// </summary>
    /// <param name="name">The name of the options instance being validated.</param>
    /// <param name="options">The options instance.</param>
    /// <returns>Validation result.</returns>
    [global::System.CodeDom.Compiler.GeneratedCodeAttribute("Microsoft.Extensions.Options.SourceGeneration", "10.0.12.23009")]
    #if !NET10_0_OR_GREATER
    [System.Diagnostics.CodeAnalysis.UnconditionalSuppressMessage("Trimming", "IL2026:RequiresUnreferencedCode",
            Justification = "The created ValidationContext object is used in a way that never call reflection")]
    #endif
    public global::Microsoft.Extensions.Options.ValidateOptionsResult Validate(string? name, global::Microsoft.Diagnostics.Tools.Monitor.MyOptions options)
    {
        global::Microsoft.Extensions.Options.ValidateOptionsResultBuilder? builder = null;
        #if NET10_0_OR_GREATER
        string displayName = string.IsNullOrEmpty(name) ? "MyOptions.Validate" : $"{name}.Validate";
        var context = new global::System.ComponentModel.DataAnnotations.ValidationContext(options, displayName, null, null);
        #else
        var context = new global::System.ComponentModel.DataAnnotations.ValidationContext(options);
        #endif

        context.MemberName = "Validate";
        context.DisplayName = string.IsNullOrEmpty(name) ? "MyOptions.Validate" : $"{name}.Validate";
        (builder ??= new()).AddResults(((global::System.ComponentModel.DataAnnotations.IValidatableObject)options).Validate(context));

        return builder is null ? global::Microsoft.Extensions.Options.ValidateOptionsResult.Success : builder.Build();
    }
}

Note that the construction of the ValidationContext passes null for the IServiceProvider parameter.

It appears that the generator does not consider if an IServiceProvider is available: https://github.com/dotnet/runtime/blob/main/src/libraries/Microsoft.Extensions.Options/gen/Emitter.cs#L697

This prevents IValidatableObject implementations from using the ValidationContext.GetService method because it will always return null. Here are a few examples where .NET Monitor uses this and would prevent it from adopting options validation source generation:

• https://github.com/dotnet/dotnet-monitor/blob/main/src/Tools/dotnet-monitor/CollectionRules/Options/ValidationHelper.cs#L40
• https://github.com/dotnet/dotnet-monitor/blob/main/src/Tools/dotnet-monitor/CollectionRules/Options/Actions/ValidateEgressProviderAttribute.cs#L25

Not to necessarily prescribe the solution, but it would be nice if the source generator would detect an IServiceProvider parameter from the primary constructor or possibly a field from the IValidateOptions<T> implementation and pass that instance when constructing the ValidationContext.

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[tarekgh]

This is currently a limitation in the options source gen. I am wondering, can't you have the MyOptions created with the service provider?

[sbomer]

Not sure if I understand the suggestion - we can have MyOptions ctor take the service provider, but the issue is that the generated code passes null as the service provider when creating the ValidationContext. If the generator could pick up the ctor parameter and pass it along, that would fix it, but without this the workaround requires writing the IValidateOptions implementation by hand.

[sbomer]

@tarekgh clarified offline that the suggested workaround is to retrieve the service collection from MyOptions directly inside of the IValidateableObject implementation (thanks!). That might work - recursively validatable types would all need to take the service collection though.