CSHARP-5793: Support Enumerable Contains and SequenceEqual with null comparer

[damieng]

Handles the scenario where, when targetting .NET 10 and using C# 14 with a non-IEquatable type will use the 3-arg versions of MemoryExtensions.Contains and MemoryExtensions.SequenceEquals passing null as the comparer.

Implementation

Now just rewrites the 2 arg versions and the 3 arg version when it is null and writes that back to the Enumerable 2 args version as our C# Provider does not handle the 3-arg versions at all.

Did this for Contains and SequenceEquals after confirming with Shay that EF probably should have the null/3-arg version remapped for SequenceEquals too.

Notes

Unlike the other 2-arg versions we can't test these directly without switching to .NET 10. The tests will for now not exercise that path but will do so when we switch to .NET 10 and C# in the future.

They have been tested with an external project. We can't add that yet due to CI limitations.

Fixes CSHARP-5749.

[rstam]

These new tests are fine.

I would also add these new tests:

    [Fact]
    public void Enumerable_Contains_with_null_comparer_should_work()
    {
        var collection = Fixture.Collection;
        var names = new[] { "Two", "Three" };

        var queryable = collection.AsQueryable().Where((C x) => names.Contains(x.Name, null));

        var results = queryable.ToArray();
        results.Select(x => x.Id).Should().Equal(2, 3);
    }

    [Fact]
    public void Enumerable_SequenceEqual_with_null_comparer_work()
    {
        var collection = Fixture.Collection;
        var ratings = new[] { 1, 9, 6 };

        var queryable = collection.AsQueryable().Where((C x) => ratings.SequenceEqual(x.Ratings, null));

        var results = queryable.ToArray();
        results.Select(x => x.Id).Should().Equal(3);
    }

[damieng]

Done.

[rstam]

If you agree with my requested changes I would change the description of CSHARP-5793 to:

Support Enumerable Contains and SequenceEqual with null comparer

It's a more general fix, because not only does it address the C# 14 issue but it also adds support for null comparer to the Enumerable methods.

[rstam]

This is not correct.

We want to go into the then clause for the WithComparer methods and throw an exception if the comparer is not null.

[rstam]

Also, I suggest creating static readonly fields __containsMethods and __containsWithComparerMethods to shorten the code and avoid extra array creation.

[damieng]

Why do we want to do that? That's a behavioral change and a custom message - it should be fine with the current message it already displays today.

[damieng]

Did the cached arrays and also did the same thing in the ClrCompat visitor too.

[damieng]

Let's leave the custom/alternate error message for cases where a non-null comparer is passed for now.

[rstam]

Same comment as above.

[damieng]

Done.

[Copilot]

Pull request overview

This PR adds support for handling Contains and SequenceEqual methods when they are called with a null comparer argument. This scenario arises in .NET 10 with C# 14 when using non-IEquatable types, where the compiler automatically uses 3-argument overloads of MemoryExtensions.Contains and MemoryExtensions.SequenceEqual with null as the comparer.

Key Changes:

• Modified translators to treat 3-arg Contains/SequenceEqual with null comparer the same as 2-arg versions
• Added QueryableMethod reflection definitions for ContainsWithComparer and SequenceEqualWithComparer
• Refactored method matching in ClrCompatExpressionRewriter to use static arrays for better maintainability

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
tests/MongoDB.Driver.Tests/Linq/Linq3Implementation/Jira/CSharp5749Tests.cs	Added test methods for enum-based Contains/SequenceEqual and null comparer scenarios; updated test fixture data model with Day and Days properties
src/MongoDB.Driver/Linq/Linq3Implementation/Translators/ExpressionToAggregationExpressionTranslators/MethodTranslators/SequenceEqualMethodToAggregationExpressionTranslator.cs	Added static method arrays and logic to handle 3-arg SequenceEqual with null comparer
src/MongoDB.Driver/Linq/Linq3Implementation/Translators/ExpressionToAggregationExpressionTranslators/MethodTranslators/ContainsMethodToAggregationExpressionTranslator.cs	Added static method arrays and logic to handle 3-arg Contains with null comparer
src/MongoDB.Driver/Linq/Linq3Implementation/Reflection/QueryableMethod.cs	Added ContainsWithComparer and SequenceEqualWithComparer method reflection definitions
src/MongoDB.Driver/Linq/Linq3Implementation/Misc/ClrCompatExpressionRewriter.cs	Refactored to use static readonly MethodInfo arrays instead of inline method checks for better performance and readability

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