support for rewriting null conditional access expressions

src/EntityFrameworkCore.Projectables.Abstractions/NullConditionalRewriteSupport.cs

@@ -0,0 +1,30 @@
+namespace EntityFrameworkCore.Projectables
+{
+    /// <summary>
+    /// Configures how null-conditional operators are handeled
+    /// </summary>
+    public enum NullConditionalRewriteSupport
+    {
+        /// <summary>
+        /// Don't rewrite null conditional operators (Default behavior).
+        /// Usage of null conditional operators is thereby not allowed
+        /// </summary>
+        None,
+
+        /// <summary>
+        /// Ignore null-conditional operators in the generated expression tree
+        /// </summary>
+        /// <remarks>
+        /// <c>(A?.B)</c> is rewritten as expression: <c>(A.B)</c>
+        /// </remarks>
+        Ignore,
+
+        /// <summary>
+        /// Translates null-conditional operators into explicit null checks
+        /// </summary>
+        /// <remarks>
+        /// <c>(A?.B)</c> is rewritten as expression: <c>(A != null ? A.B : null)</c>
+        /// </remarks>
+        Rewrite
+    }
+}

src/EntityFrameworkCore.Projectables.Abstractions/ProjectableAttribute.cs

@@ -9,5 +9,6 @@ namespace EntityFrameworkCore.Projectables
     [AttributeUsage(AttributeTargets.Method | AttributeTargets.Property, Inherited = true, AllowMultiple = false)]
     public sealed class ProjectableAttribute : Attribute
     {
+        public NullConditionalRewriteSupport NullConditionalRewriteSupport { get; set; }
     }
 }

src/EntityFrameworkCore.Projectables.Generator/EntityFrameworkCore.Projectables.Generator.csproj

@@ -7,6 +7,7 @@
   </PropertyGroup>
 
   <ItemGroup>
+    <Compile Include="..\EntityFrameworkCore.Projectables.Abstractions\NullConditionalRewriteSupport.cs" Link="NullConditionalRewriteSupport.cs" />
     <Compile Include="..\EntityFrameworkCore.Projectables\Services\ProjectionExpressionClassNameGenerator.cs" Link="ProjectionExpressionClassNameGenerator.cs" />
   </ItemGroup>
 

src/EntityFrameworkCore.Projectables.Generator/ExpressionSyntaxRewriter.cs

@@ -14,11 +14,76 @@ namespace EntityFrameworkCore.Projectables.Generator
     {
         readonly INamedTypeSymbol _targetTypeSymbol;
         readonly SemanticModel _semanticModel;
+        readonly NullConditionalRewriteSupport _nullConditionalRewriteSupport;
+        readonly Stack<ExpressionSyntax> _conditionalAccessExpressionsStack = new();
 
-        public ExpressionSyntaxRewriter(INamedTypeSymbol targetTypeSymbol, SemanticModel semanticModel)
+        public ExpressionSyntaxRewriter(INamedTypeSymbol targetTypeSymbol, SemanticModel semanticModel, NullConditionalRewriteSupport nullConditionalRewriteSupport)
         {
             _targetTypeSymbol = targetTypeSymbol;
             _semanticModel = semanticModel;
+            _nullConditionalRewriteSupport = nullConditionalRewriteSupport;
+        }
+
+        public override SyntaxNode? VisitConditionalAccessExpression(ConditionalAccessExpressionSyntax node)
+        {
+            var targetExpression = (ExpressionSyntax)Visit(node.Expression);
+
+            _conditionalAccessExpressionsStack.Push(targetExpression);
+
+            return _nullConditionalRewriteSupport switch {
+                NullConditionalRewriteSupport.Ignore => Visit(node.WhenNotNull),
+                NullConditionalRewriteSupport.Rewrite =>
+                    SyntaxFactory.ConditionalExpression(
+                        SyntaxFactory.BinaryExpression(
+                            SyntaxKind.NotEqualsExpression,
+                            targetExpression
+                                .WithTrailingTrivia(SyntaxFactory.Whitespace(" ")),
+                            SyntaxFactory.LiteralExpression(SyntaxKind.NullLiteralExpression)
+                                .WithLeadingTrivia(SyntaxFactory.Whitespace(" "))
+                        )
+                            .WithTrailingTrivia(SyntaxFactory.Whitespace(" ")),
+                        SyntaxFactory.ParenthesizedExpression(
+                            (ExpressionSyntax)Visit(node.WhenNotNull)
+                        )
+                            .WithLeadingTrivia(SyntaxFactory.Whitespace(" "))
+                            .WithTrailingTrivia(SyntaxFactory.Whitespace(" ")),
+                        SyntaxFactory.LiteralExpression(SyntaxKind.NullLiteralExpression)
+                            .WithLeadingTrivia(SyntaxFactory.Whitespace(" "))
+                    ),
+                _ => base.VisitConditionalAccessExpression(node)
+            };
+        }
+
+        public override SyntaxNode? VisitMemberBindingExpression(MemberBindingExpressionSyntax node)
+        {
+            if (_conditionalAccessExpressionsStack.Count == 0)
+            {
+                throw new InvalidOperationException("Expected at least one conditional expression on the stack");
+            }
+
+            var targetExpression = _conditionalAccessExpressionsStack.Pop();
+
+            return _nullConditionalRewriteSupport switch {
+                NullConditionalRewriteSupport.Ignore => SyntaxFactory.MemberAccessExpression(SyntaxKind.SimpleMemberAccessExpression, targetExpression, node.Name),
+                NullConditionalRewriteSupport.Rewrite => SyntaxFactory.MemberAccessExpression(SyntaxKind.SimpleMemberAccessExpression, targetExpression, node.Name),
+                _ => node
+            };
+        }
+
+        public override SyntaxNode? VisitElementBindingExpression(ElementBindingExpressionSyntax node)
+        {
+            if (_conditionalAccessExpressionsStack.Count == 0)
+            {
+                throw new InvalidOperationException("Expected at least one conditional expression on the stack");
+            }
+
+            var targetExpression = _conditionalAccessExpressionsStack.Pop();
+
+            return _nullConditionalRewriteSupport switch {
+                NullConditionalRewriteSupport.Ignore => SyntaxFactory.ElementAccessExpression(targetExpression, node.ArgumentList),
+                NullConditionalRewriteSupport.Rewrite => SyntaxFactory.ElementAccessExpression(targetExpression, node.ArgumentList),
+                _ => Visit(node)
+            };
         }
 
         public override SyntaxNode? VisitMemberAccessExpression(MemberAccessExpressionSyntax node)

src/EntityFrameworkCore.Projectables.Generator/ProjectableInterpreter.cs

@@ -1,4 +1,5 @@
-using System.Collections.Generic;
+using System;
+using System.Collections.Generic;
 using System.Linq;
 using Microsoft.CodeAnalysis;
 using Microsoft.CodeAnalysis.CSharp;
@@ -31,7 +32,6 @@ namespace EntityFrameworkCore.Projectables.Generator
                 return null;
             }
 
-
             var projectableAttributeTypeSymbol = context.Compilation.GetTypeByMetadataName("EntityFrameworkCore.Projectables.ProjectableAttribute");
 
             var projectableAttributeClass = memberSymbol.GetAttributes()
@@ -43,7 +43,15 @@ namespace EntityFrameworkCore.Projectables.Generator
                 return null;
             }
 
-            var expressionSyntaxRewriter = new ExpressionSyntaxRewriter(memberSymbol.ContainingType, semanticModel);
+            var nullConditionalRewriteSupport = projectableAttributeClass.NamedArguments
+                .Where(x => x.Key == "NullConditionalRewriteSupport")
+                .Where(x => x.Value.Kind == TypedConstantKind.Enum)
+                .Select(x => x.Value.Value)
+                .Where(x => Enum.IsDefined(typeof(NullConditionalRewriteSupport), x))
+                .Cast<NullConditionalRewriteSupport>()
+                .FirstOrDefault();
+
+            var expressionSyntaxRewriter = new ExpressionSyntaxRewriter(memberSymbol.ContainingType, semanticModel, nullConditionalRewriteSupport);
             var parameterSyntaxRewriter = new ParameterSyntaxRewriter(semanticModel);
             var returnTypeSyntaxRewriter = new ReturnTypeSyntaxRewriter(semanticModel);
 
@@ -128,8 +136,6 @@ namespace EntityFrameworkCore.Projectables.Generator
                 return null;
             }
 
-
-
             descriptor.UsingDirectives =
                 memberDeclarationSyntax.SyntaxTree
                     .GetRoot()
@@ -137,7 +143,6 @@ namespace EntityFrameworkCore.Projectables.Generator
                     .OfType<UsingDirectiveSyntax>()
                     .Select(x => x.ToString());
 
-
             return descriptor;
         }
     }