CSHARP-5436: Optimize special case of Any with constant array and fie…

src/MongoDB.Driver/Linq/Linq3Implementation/Ast/Optimizers/AstSimplifier.cs

@@ -103,6 +103,53 @@ static bool OperatorMapsNullToNull(AstUnaryOperator @operator)
             }
         }
 
+        public override AstNode VisitExprFilter(AstExprFilter node)
+        {
+            var optimizedNode = base.VisitExprFilter(node);
+
+            if (optimizedNode is AstExprFilter exprFilter &&
+                exprFilter.Expression is AstUnaryExpression unaryExpression &&
+                unaryExpression.Operator == AstUnaryOperator.AnyElementTrue &&
+                unaryExpression.Arg is AstMapExpression mapExpression &&
+                mapExpression.Input is AstConstantExpression inputConstant &&
+                inputConstant.Value is BsonArray inputArrayValue &&
+                mapExpression.In is AstBinaryExpression inBinaryExpression &&
+                inBinaryExpression.Operator == AstBinaryOperator.Eq &&
+                TryGetBinaryExpressionArguments(inBinaryExpression, out AstFieldPathExpression fieldPathExpression, out AstVarExpression varExpression) &&
+                fieldPathExpression.Path.Length > 1 && fieldPathExpression.Path[0] == '$' && fieldPathExpression.Path[1] != '$' &&
+                varExpression == mapExpression.As)
+            {
+                // { $expr : { $anyElementTrue : { $map : { input : <constantArray>, as : "<var>", in : { $eq : ["$<dottedFieldName>", "$$<var>"] } } } } }
+                //      => { "<dottedFieldName>" : { $in : <constantArray> } }
+                return AstFilter.In(AstFilter.Field(fieldPathExpression.Path.Substring(1)), inputArrayValue);
+            }
+
+            return optimizedNode;
+
+            static bool TryGetBinaryExpressionArguments<T1, T2>(AstBinaryExpression binaryExpression, out T1 arg1, out T2 arg2)
+                where T1 : AstNode
+                where T2 : AstNode
+            {
+                if (binaryExpression.Arg1 is T1 arg1AsT1 && binaryExpression.Arg2 is T2 arg2AsT2)
+                {
+                    arg1 = arg1AsT1;
+                    arg2 = arg2AsT2;
+                    return true;
+                }
+
+                if (binaryExpression.Arg1 is T2 arg1AsT2 && binaryExpression.Arg1 is T1 arg2AsT1)
+                {
+                    arg1 = arg2AsT1;
+                    arg2 = arg1AsT2;
+                    return true;
+                }
+
+                arg1 = null;
+                arg2 = null;
+                return false;
+            }
+        }
+
         public override AstNode VisitFieldOperationFilter(AstFieldOperationFilter node)
         {
             node = (AstFieldOperationFilter)base.VisitFieldOperationFilter(node);

tests/MongoDB.Driver.Tests/Linq/Linq3Implementation/Translators/ExpressionToAggregationExpressionTranslators/MethodTranslators/AnyMethodToAggregationExpressionTranslatorTests.cs

@@ -59,6 +59,22 @@ public void Any_with_predicate_should_work(
             results.Should().Equal(false, false, false, true);
         }
 
+        [Fact]
+        public void Any_on_constant_array_should_be_optimized()
+        {
+            var collection = CreateCollection();
+
+            var obj = new[] { 1, 2, 3 };
+            var queryable = collection.AsQueryable()
+                .Where(x => obj.Any(y => x.Id == y));
+
+            var stages = Translate(collection, queryable);
+            AssertStages(stages, "{ $match : { _id : { $in : [1, 2, 3] } } }");
+
+            var results = queryable.ToList();
+            results.Select(x => x.Id).Should().Equal(1, 2, 3);
+        }
+
         private IMongoCollection<C> CreateCollection()
         {
             var collection = GetCollection<C>("test");