Reimplement entity equality

[roji]

New implementation of entity equality rewriter, which follows exact entity (and anonymous) from roots to the comparison expression, for more precise rewriting.

Note that unlike the first attempt in #15823, the visitors in this PR are completely stateless.

Closes #15588

Additional scoped-out items (excluding enhancements we probably won't do for 3.0):

• Rewrite Contains() and OrderBy() support (Entity Equality: rewrite Contains, OrderBy #15939)
• Owned entity support (Entity Equality: owned entity support #15936)
• GroupBy support (Entity Equality: support GroupBy #15938)
• Cardinality-reducing methods accepting IQueryable and returning superclass/subclass of T (Reimplement entity equality #15920 (comment))
• Possibly: complex EE cases (QueryRewrite: implement complex cases of entity equality and enable relevant tests #15260)

[roji]

(will check failing tests tomorrow, in the meantime a review would be great)

[roji]

And one last comment before I'm off... Near the end of this refactor I realized that the EntityReferenceExpression nodes can probably be reduced during the first visit, obviating a second reduce-only pass. I'll look at that tomorrow.

[smitpatel]

Was gonna just that only. You don't need reducing visitor. Just top level method to unwrap the custom expression.

We probably need to do the same for nav expansion too.

[roji]

@smitpatel yep :) It took me a while but I did get it in the end...

[maumar]

@roji you can also remove entity equality code from nav expansion (NavigationExpandingVisitor.VisitBinary + CreateNullComparisonArguments) to make sure the new logic covers all the scenarios

[roji]

@maumar done, 0 test failures after removing that code :)

[roji]

OK guys, I think it's done.

The visitor now reduces nodes as it does its pass, no more 2nd reducing pass. There are also a ton more fixes and cleanups - it may need to be reviewed fully again. Sorry for all the back-and-forths on this, hopefully my future query PRs will be more quick and direct to the point.

[maumar]

what about: ctx.Customers.OfType<VipCustomer>().FirstOrDefault<Customer>(), i.e. when type argument of cardinality reducing operator is explicitly defined and different than one on source?

[roji]

Hmm, interesting - I've never seen someone call FirstOrDefault with an explicit type parameter, any specific value in doing so?

[maumar]

can't think of anything reasonable where the result would be an entity but I'm working on a somewhat similar problem in different area (#15535), where the First method was typed as object. Might be worth adding test just in case. We have some inheritance in GearsOfWar model (Faction entity) that can be used for that purpose.

[roji]

Am deferring this for now (made a note at the top post) so that I can merge this PR quickly. Will get around to it soon.