CSHARP-5572: Implement new KnownSerializerFinder

src/MongoDB.Bson/Serialization/IBsonSerializerExtensions.cs

@@ -50,6 +50,38 @@ public static TValue Deserialize<TValue>(this IBsonSerializer<TValue> serializer
             return serializer.Deserialize(context, args);
         }
 
+        /// <summary>
+        /// Gets the serializer for a base type starting from a serializer for a derived type.
+        /// </summary>
+        /// <param name="serializer">The serializer for the derived type.</param>
+        /// <param name="baseType">The base type.</param>
+        /// <returns>The serializer for the base type.</returns>
+        public static IBsonSerializer GetBaseTypeSerializer(this IBsonSerializer serializer, Type baseType)
+        {
+            if (!baseType.IsAssignableFrom(serializer.ValueType))
+            {
+                throw new ArgumentException($"{baseType} is not assignable from {serializer.ValueType}.");
+            }
+
+            return BsonSerializer.LookupSerializer(baseType); // TODO: should be able to navigate from serializer
+        }
+
+        /// <summary>
+        /// Gets the serializer for a derived type starting from a serializer for a base type.
+        /// </summary>
+        /// <param name="serializer">The serializer for the base type.</param>
+        /// <param name="derivedType">The derived type.</param>
+        /// <returns>The serializer for the derived type.</returns>
+        public static IBsonSerializer GetDerivedTypeSerializer(this IBsonSerializer serializer, Type derivedType)
+        {
+            if (!serializer.ValueType.IsAssignableFrom(derivedType))
+            {
+                throw new ArgumentException($"{serializer.ValueType} is not assignable from {derivedType}.");
+            }
+
+            return BsonSerializer.LookupSerializer(derivedType); // TODO: should be able to navigate from serializer
+        }
+
         /// <summary>
         /// Gets the discriminator convention for a serializer.
         /// </summary>

src/MongoDB.Bson/Serialization/Serializers/NullableSerializer.cs

@@ -33,6 +33,73 @@ public interface INullableSerializer
     /// </summary>
     public static class NullableSerializer
     {
+        private readonly static IBsonSerializer __nullableBooleanInstance = new NullableSerializer<bool>(BooleanSerializer.Instance);
+        private readonly static IBsonSerializer __nullableDecimalInstance = new NullableSerializer<decimal>(DecimalSerializer.Instance);
+        private readonly static IBsonSerializer __nullableDecimal128Instance = new NullableSerializer<Decimal128>(Decimal128Serializer.Instance);
+        private readonly static IBsonSerializer __nullableDoubleInstance = new NullableSerializer<double>(DoubleSerializer.Instance);
+        private readonly static IBsonSerializer __nullableInt32Instance = new NullableSerializer<int>(Int32Serializer.Instance);
+        private readonly static IBsonSerializer __nullableInt64Instance = new NullableSerializer<long>(Int64Serializer.Instance);
+        private readonly static IBsonSerializer __nullableLocalDateTimeInstance = new NullableSerializer<DateTime>(DateTimeSerializer.LocalInstance);
+        private readonly static IBsonSerializer __nullableObjectIdInstance = new NullableSerializer<ObjectId>(ObjectIdSerializer.Instance);
+        private readonly static IBsonSerializer __nullableSingleInstance = new NullableSerializer<float>(SingleSerializer.Instance);
+        private readonly static IBsonSerializer __nullableStandardGuidInstance = new NullableSerializer<Guid>(GuidSerializer.StandardInstance);
+        private readonly static IBsonSerializer __nullableUtcDateTimeInstance = new NullableSerializer<DateTime>(DateTimeSerializer.UtcInstance);
+
+        /// <summary>
+        /// Gets a serializer for nullable bools.
+        /// </summary>
+        public static IBsonSerializer NullableBooleanInstance => __nullableBooleanInstance;
+
+        /// <summary>
+        /// Gets a serializer for nullable decimals.
+        /// </summary>
+        public static IBsonSerializer NullableDecimalInstance => __nullableDecimalInstance;
+
+        /// <summary>
+        /// Gets a serializer for nullable Decimal128s.
+        /// </summary>
+        public static IBsonSerializer NullableDecimal128Instance => __nullableDecimal128Instance;
+
+        /// <summary>
+        /// Gets a serializer for nullable doubles.
+        /// </summary>
+        public static IBsonSerializer NullableDoubleInstance => __nullableDoubleInstance;
+
+        /// <summary>
+        /// Gets a serializer for nullable ints.
+        /// </summary>
+        public static IBsonSerializer NullableInt32Instance => __nullableInt32Instance;
+
+        /// <summary>
+        /// Gets a serializer for nullable longs.
+        /// </summary>
+        public static IBsonSerializer NullableInt64Instance => __nullableInt64Instance;
+
+        /// <summary>
+        /// Gets a serializer for local DateTime.
+        /// </summary>
+        public static IBsonSerializer NullableLocalDateTimeInstance => __nullableLocalDateTimeInstance;
+
+        /// <summary>
+        /// Gets a serializer for nullable floats.
+        /// </summary>
+        public static IBsonSerializer NullableSingleInstance => __nullableSingleInstance;
+
+        /// <summary>
+        /// Gets a serializer for nullable ObjectIds.
+        /// </summary>
+        public static IBsonSerializer NullableObjectIdInstance => __nullableObjectIdInstance;
+
+        /// <summary>
+        /// Gets a serializer for nullable Guids with standard representation.
+        /// </summary>
+        public static IBsonSerializer NullableStandardGuidInstance => __nullableStandardGuidInstance;
+
+        /// <summary>
+        /// Gets a serializer for UTC DateTime.
+        /// </summary>
+        public static IBsonSerializer NullableUtcDateTimeInstance => __nullableUtcDateTimeInstance;
+
         /// <summary>
         /// Creates a NullableSerializer.
         /// </summary>

src/MongoDB.Driver/Linq/Linq3Implementation/ExtensionMethods/ExpressionExtensions.cs

@@ -60,5 +60,17 @@ public static TValue GetConstantValue<TValue>(this Expression expression, Expres
             var message = $"Expression must be a constant: {expression} in {containingExpression}.";
             throw new ExpressionNotSupportedException(message);
         }
+
+        public static bool IsConvert(this Expression expression, out Expression operand)
+        {
+            if (expression is UnaryExpression { NodeType: ExpressionType.Convert } unaryExpression)
+            {
+                operand = unaryExpression.Operand;
+                return true;
+            }
+
+            operand = null;
+            return false;
+        }
     }
 }

src/MongoDB.Driver/Linq/Linq3Implementation/GroupingWithOutputExpressionStageDefinitions.cs

@@ -64,7 +64,8 @@ private AstStage RenderProjectStage(
             out IBsonSerializer<TOutput> outputSerializer)
         {
             var partiallyEvaluatedOutput = (Expression<Func<TGrouping, TOutput>>)PartialEvaluator.EvaluatePartially(_output);
-            var context = TranslationContext.Create(translationOptions);
+            var parameter = partiallyEvaluatedOutput.Parameters.Single();
+            var context = TranslationContext.Create(partiallyEvaluatedOutput, initialNode: parameter, initialSerializer: inputSerializer, translationOptions: translationOptions);
             var outputTranslation = ExpressionToAggregationExpressionTranslator.TranslateLambdaBody(context, partiallyEvaluatedOutput, inputSerializer, asRoot: true);
             var (projectStage, projectSerializer) = ProjectionHelper.CreateProjectStage(outputTranslation);
             outputSerializer = (IBsonSerializer<TOutput>)projectSerializer;
@@ -106,7 +107,8 @@ protected override AstStage RenderGroupingStage(
             out IBsonSerializer<IGrouping<TValue, TInput>> groupingOutputSerializer)
         {
             var partiallyEvaluatedGroupBy = (Expression<Func<TInput, TValue>>)PartialEvaluator.EvaluatePartially(_groupBy);
-            var context = TranslationContext.Create(translationOptions);
+            var parameter = partiallyEvaluatedGroupBy.Parameters.Single();
+            var context = TranslationContext.Create(partiallyEvaluatedGroupBy, initialNode: parameter, initialSerializer: inputSerializer, translationOptions: translationOptions);
             var groupByTranslation = ExpressionToAggregationExpressionTranslator.TranslateLambdaBody(context, partiallyEvaluatedGroupBy, inputSerializer, asRoot: true);
 
             var valueSerializer = (IBsonSerializer<TValue>)groupByTranslation.Serializer;
@@ -150,7 +152,8 @@ protected override AstStage RenderGroupingStage(
             out IBsonSerializer<IGrouping<AggregateBucketAutoResultId<TValue>, TInput>> groupingOutputSerializer)
         {
             var partiallyEvaluatedGroupBy = (Expression<Func<TInput, TValue>>)PartialEvaluator.EvaluatePartially(_groupBy);
-            var context = TranslationContext.Create(translationOptions);
+            var parameter = partiallyEvaluatedGroupBy.Parameters.Single();
+            var context = TranslationContext.Create(partiallyEvaluatedGroupBy, initialNode: parameter, initialSerializer: inputSerializer, translationOptions: translationOptions);
             var groupByTranslation = ExpressionToAggregationExpressionTranslator.TranslateLambdaBody(context, partiallyEvaluatedGroupBy, inputSerializer, asRoot: true);
 
             var valueSerializer = (IBsonSerializer<TValue>)groupByTranslation.Serializer;
@@ -188,7 +191,8 @@ protected override AstStage RenderGroupingStage(
             out IBsonSerializer<IGrouping<TValue, TInput>> groupingOutputSerializer)
         {
             var partiallyEvaluatedGroupBy = (Expression<Func<TInput, TValue>>)PartialEvaluator.EvaluatePartially(_groupBy);
-            var context = TranslationContext.Create(translationOptions);
+            var parameter = partiallyEvaluatedGroupBy.Parameters.Single();
+            var context = TranslationContext.Create(partiallyEvaluatedGroupBy, initialNode: parameter, initialSerializer: inputSerializer, translationOptions: translationOptions);
             var groupByTranslation = ExpressionToAggregationExpressionTranslator.TranslateLambdaBody(context, partiallyEvaluatedGroupBy, inputSerializer, asRoot: true);
             var pushElements = AstExpression.AccumulatorField("_elements", AstUnaryAccumulatorOperator.Push, AstExpression.RootVar);
             var groupBySerializer = (IBsonSerializer<TValue>)groupByTranslation.Serializer;

src/MongoDB.Driver/Linq/Linq3Implementation/KnownSerializerFinders/KnownSerializerFinder.cs

@@ -0,0 +1,82 @@
+/* Copyright 2010-present MongoDB Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+using System.Linq.Expressions;
+using MongoDB.Bson.Serialization;
+
+namespace MongoDB.Driver.Linq.Linq3Implementation.KnownSerializerFinders;
+
+internal static class KnownSerializerFinder
+{
+    public static KnownSerializerMap FindKnownSerializers(
+        Expression expression)
+    {
+        var knownSerializers = new KnownSerializerMap();
+        return FindKnownSerializers(expression, knownSerializers);
+    }
+
+    public static KnownSerializerMap FindKnownSerializers(
+        Expression expression,
+        Expression initialNode,
+        IBsonSerializer knownSerializer)
+    {
+        var knownSerializers = new KnownSerializerMap();
+        knownSerializers.AddSerializer(initialNode, knownSerializer);
+        return FindKnownSerializers(expression, knownSerializers);
+    }
+
+    public static KnownSerializerMap FindKnownSerializers(
+        Expression expression,
+        (Expression Node, IBsonSerializer KnownSerializer)[] initialNodes)
+    {
+        var knownSerializers = new KnownSerializerMap();
+        foreach (var (initialNode, knownSerializer) in initialNodes)
+        {
+            knownSerializers.AddSerializer(initialNode, knownSerializer);
+
+        }
+        return FindKnownSerializers(expression, knownSerializers);
+    }
+
+    public static KnownSerializerMap FindKnownSerializers(
+        Expression expression,
+        KnownSerializerMap knownSerializers)
+    {
+        var visitor = new KnownSerializerFinderVisitor(knownSerializers);
+
+        int oldSerializerCount;
+        int newSerializerCount;
+        do
+        {
+            visitor.StartNextPass();
+            oldSerializerCount = knownSerializers.Count;
+            visitor.Visit(expression);
+            newSerializerCount = knownSerializers.Count;
+
+            // TODO: prevent infinite loop, throw after 100000 passes?
+        }
+        while (visitor.Pass == 1 || newSerializerCount > oldSerializerCount); // I don't know yet if this can be done in a single pass
+
+        //#if DEBUG
+        var expressionWithUnknownSerializer = UnknownSerializerFinder.FindExpressionWithUnknownSerializer(expression, knownSerializers);
+        if (expressionWithUnknownSerializer != null)
+        {
+            throw new ExpressionNotSupportedException(expressionWithUnknownSerializer, because: "we were unable to determine which serializer to use for the result");
+        }
+        //#endif
+
+        return knownSerializers;
+    }
+}