Configuration of IJsonAssertionOptions slows down comparison a log

[labsin]

To check doubles using precision when comparing JSON's, I am using the following options callback in BeEquivalentTo:

options => options.Using<double>(d => d.Subject.Should().BeApproximately(d.Expectation, 0.001))
  .WhenTypeIs<double>()

But it seems that this builder callback is being called for every value comparison.
JTokenDifferentiator.CompareValues contains:

using (var scope = new AssertionScope())
{
    actual.Value.Should().BeEquivalentTo(expected.Value, options =>
        (JsonAssertionOptions<object>)config.Invoke(new JsonAssertionOptions<object>(options)));

    hasMismatches = scope.Discard().Length > 0;
}

With the addition of the Using, a bigger json (MB's) goes from 200ms to +10s on my PC.

As a workaround, I replicated the behavior of the builder by accessing the userEquivalencySteps field on SelfReferenceEquivalencyAssertionOptions using reflection and inserting a custom IEquivalencyStep, instead of using the fluent API.
This brings it to 1s, which is acceptable for my use case.

Would it make sense to not call this options callback for every JSON value and build it once?
Or would adding API to add a custom IEquivalencyStep instead of the builder make sense?

[dennisdoomen]

Thanks. Which version have you been using?

[labsin]

Was using FluentAssertion.Json 6.1, but also happening on 8.0

I tried fixing the issue, but I cannot do it using only the public API.

I tried:

1 Just passing a cached options to BeEquivalentTo: is not ideal because it still clones the default options on every invocation, which is still slow if done many times
2 Replicating the behavior of BeEquivalentTo: is not possible cause EquivalencyValidator is not public API
3 Implementing a new EquivalencyValidator cause it is not possible to implement INote because it has an internal setter

To come back on 3, the relevant part of the IValidateChildNodeEquivalency for JValues is to loop over AssertionConfiguration.Current.Equivalency.Plan. This needs a IEquivalencyValidationContext, which needs an INode.

As the JValue is actually just a single value and never a collection, all I actually need for the comparison using the options, is the loop over AssertionConfiguration.Current.Equivalency.Plan, but IEquivalencyStep.Handle needs a IEquivalencyValidationContext and an IValidateChildNodeEquivalency which is not possible using public API

[labsin]

Pushed what I tried to https://github.com/labsin/fluentassertions.json/tree/slow_compare

It uses reflection, so I didn't open a PR.

Would a better solution be to actually implement validation steps for the Json objects and maybe make needed api public?

[dennisdoomen]

Did you do an analysis to see which part is slow? Because the call to BeEquivalentTo is the core of the entire analysis.