CSHARP-2460: Add throwing exception if linq expressions use unreachable query members.

Author: DmitryLukyanov

src/MongoDB.Driver/Linq/Expressions/FieldExpression.cs

@@ -20,12 +20,13 @@
 
 namespace MongoDB.Driver.Linq.Expressions
 {
-    internal sealed class FieldExpression : SerializationExpression, IFieldExpression
+    internal sealed class FieldExpression : SerializationExpression, IFieldExpression, IHasOutOfCurrentScopePrefix
     {
         private readonly Expression _document;
         private readonly string _fieldName;
         private readonly Expression _original;
         private readonly IBsonSerializer _serializer;
+        private string _outOfCurrentScopePrefix;
 
         public FieldExpression(string fieldName, IBsonSerializer serializer)
             : this(null, fieldName, serializer, null)
@@ -70,6 +71,12 @@ public Expression Original
             get { return _original; }
         }
 
+        public string OutOfCurrentScopePrefix
+        {
+            get { return _outOfCurrentScopePrefix; }
+            set { _outOfCurrentScopePrefix = value; }
+        }
+
         public override IBsonSerializer Serializer
         {
             get { return _serializer; }

src/MongoDB.Driver/Linq/Expressions/IHasOutOfCurrentScopePrefix.cs

@@ -0,0 +1,22 @@
+/* Copyright 2019-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.
+*/
+
+namespace MongoDB.Driver.Linq.Expressions
+{
+    internal interface IHasOutOfCurrentScopePrefix
+    {
+        string OutOfCurrentScopePrefix { get; set; }
+    }
+}

src/MongoDB.Driver/Linq/Processors/OutOfCurrentScopePrefixCollector.cs

@@ -0,0 +1,52 @@
+/* Copyright 2019-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.Collections.Generic;
+using System.Linq.Expressions;
+using MongoDB.Driver.Linq.Expressions;
+
+namespace MongoDB.Driver.Linq.Processors
+{
+    /// <summary>
+    /// The expression visitor to collect all expression fields which have been defined out of the current scope.
+    /// </summary>
+    internal sealed class OutOfCurrentScopePrefixCollector : ExtensionExpressionVisitor
+    {
+        private readonly HashSet<string> _outOfCurrentScopePrefixCollection = new HashSet<string>();
+
+        /// <summary>
+        /// Collects the list of expression fields which have been defined out of the current scope.
+        /// </summary>
+        /// <param name="expression">The expression.</param>
+        /// <returns>The result collection.</returns>
+        public static IEnumerable<string> Collect(Expression expression)
+        {
+            var outOfScopePrefixCollection = new OutOfCurrentScopePrefixCollector();
+            outOfScopePrefixCollection.Visit(expression);
+            return outOfScopePrefixCollection._outOfCurrentScopePrefixCollection;
+        }
+
+        public override Expression Visit(Expression node)
+        {
+            var hasOutOfCurrentScopePrefix = node as IHasOutOfCurrentScopePrefix;
+            if (hasOutOfCurrentScopePrefix != null && !string.IsNullOrWhiteSpace(hasOutOfCurrentScopePrefix.OutOfCurrentScopePrefix))
+            {
+                _outOfCurrentScopePrefixCollection.Add(hasOutOfCurrentScopePrefix.OutOfCurrentScopePrefix);
+            }
+
+            return base.Visit(node);
+        }
+    }
+}

src/MongoDB.Driver/Linq/Processors/SerializationBinder.cs

@@ -15,14 +15,12 @@
 
 using System;
 using System.Collections.Generic;
-using System.Linq;
 using System.Linq.Expressions;
 using System.Reflection;
 using MongoDB.Bson;
 using MongoDB.Bson.Serialization;
 using MongoDB.Driver.Linq.Expressions;
 using MongoDB.Driver.Linq.Processors.EmbeddedPipeline;
-using MongoDB.Driver.Support;
 
 namespace MongoDB.Driver.Linq.Processors
 {
@@ -37,6 +35,7 @@ public static Expression Bind(Expression node, IBindingContext context, bool isC
         private readonly IBindingContext _bindingContext;
         private bool _isInEmbeddedPipeline;
         private readonly bool _isClientSideProjection;
+        private bool _isOutOfCurrentScope;
 
         private SerializationBinder(IBindingContext bindingContext, bool isClientSideProjection)
         {
@@ -103,12 +102,21 @@ protected override Expression VisitConstant(ConstantExpression node)
 
         protected override Expression VisitLambda<T>(Expression<T> node)
         {
+            var oldIsOutOfCurrentScope = _isOutOfCurrentScope;
+            if (_isInEmbeddedPipeline)
+            {
+                _isOutOfCurrentScope = true;
+            }
+
             // Don't visit the parameters. We cannot replace a parameter expression
             // with a document and we don't have a new parameter type to use because
             // we don't know why we are binding yet.
-            return node.Update(
+            var result = node.Update(
                 Visit(node.Body),
                 node.Parameters);
+            _isOutOfCurrentScope = oldIsOutOfCurrentScope;
+
+            return result;
         }
 
         protected override Expression VisitMember(MemberExpression node)
@@ -151,6 +159,12 @@ protected override Expression VisitMember(MemberExpression node)
                                 mex);
                         }
                     }
+
+                    var parameterExpression = (node.Expression as ParameterExpression);
+                    if (_isOutOfCurrentScope && parameterExpression != null)
+                    {
+                        SetOutOfCurrentScopePrefixIfPossible(newNode, parameterExpression.Name);
+                    }
                 }
             }
 
@@ -397,5 +411,14 @@ private Expression BindClientSideProjector(MethodCallExpression node)
 
             return node;
         }
+
+        private void SetOutOfCurrentScopePrefixIfPossible(Expression expression, string value)
+        {
+            var hasOutOfCurrentScopePrefix = expression as IHasOutOfCurrentScopePrefix;
+            if (hasOutOfCurrentScopePrefix != null)
+            {
+                hasOutOfCurrentScopePrefix.OutOfCurrentScopePrefix = value;
+            }
+        }
     }
 }

src/MongoDB.Driver/Linq/Translators/PredicateTranslator.cs

@@ -921,6 +921,8 @@ private FilterDefinition<BsonDocument> TranslatePipelineAny(PipelineExpression n
                 return null;
             }
 
+            ValidatePipelineExpressionThrowIfNotValid(whereExpression);
+
             FilterDefinition<BsonDocument> filter;
             var renderWithoutElemMatch = CanAnyBeRenderedWithoutElemMatch(whereExpression.Predicate);
 
@@ -1653,6 +1655,16 @@ private IFieldExpression GetFieldExpression(Expression expression)
             return fieldExpression;
         }
 
+        private void ValidatePipelineExpressionThrowIfNotValid(WhereExpression whereExpression)
+        {
+            var outOfCurrentScopePrefixCollection = OutOfCurrentScopePrefixCollector.Collect(whereExpression)?.ToList();
+            var unsupportedField = outOfCurrentScopePrefixCollection?.FirstOrDefault();
+            if (unsupportedField != null)
+            {
+                throw new NotSupportedException($"The LINQ expression: {whereExpression} has the member \"{unsupportedField}\" which can not be used to build a correct MongoDB query.");
+            }
+        }
+
         // nested types
         private class DocumentToFieldConverter : ExtensionExpressionVisitor
         {