Add support for dictionary index initializers in expressions

src/EntityFrameworkCore.Projectables.Generator/ExpressionSyntaxRewriter.cs

@@ -385,7 +385,63 @@ public ExpressionSyntaxRewriter(INamedTypeSymbol targetTypeSymbol, NullCondition
 
             return base.VisitNullableType(node);
         }
-
+
+        public override SyntaxNode? VisitInitializerExpression(InitializerExpressionSyntax node)
+        {
+            // Only handle object initializers that might contain indexer assignments
+            if (!node.IsKind(SyntaxKind.ObjectInitializerExpression))
+            {
+                return base.VisitInitializerExpression(node);
+            }
+
+            // Check if any expression is an indexer assignment (e.g., ["key"] = value)
+            var hasIndexerAssignment = node.Expressions.Any(e => 
+                e is AssignmentExpressionSyntax { Left: ImplicitElementAccessSyntax });
+
+            if (!hasIndexerAssignment)
+            {
+                return base.VisitInitializerExpression(node);
+            }
+
+            var newExpressions = new SeparatedSyntaxList<ExpressionSyntax>();
+
+            foreach (var expression in node.Expressions)
+            {
+                if (expression is AssignmentExpressionSyntax assignment &&
+                    assignment.Left is ImplicitElementAccessSyntax implicitElementAccess)
+                {
+                    // Transform ["key"] = value into { "key", value }
+                    var arguments = new SeparatedSyntaxList<ExpressionSyntax>();
+
+                    foreach (var argument in implicitElementAccess.ArgumentList.Arguments)
+                    {
+                        var visitedArgument = (ExpressionSyntax?)Visit(argument.Expression) ?? argument.Expression;
+                        arguments = arguments.Add(visitedArgument);
+                    }
+
+                    var visitedValue = (ExpressionSyntax?)Visit(assignment.Right) ?? assignment.Right;
+                    arguments = arguments.Add(visitedValue);
+
+                    var complexElementInitializer = SyntaxFactory.InitializerExpression(
+                        SyntaxKind.ComplexElementInitializerExpression,
+                        arguments
+                    );
+
+                    newExpressions = newExpressions.Add(complexElementInitializer);
+                }
+                else
+                {
+                    var visitedExpression = (ExpressionSyntax?)Visit(expression) ?? expression;
+                    newExpressions = newExpressions.Add(visitedExpression);
+                }
+            }
+
+            return SyntaxFactory.InitializerExpression(
+                SyntaxKind.CollectionInitializerExpression,
+                newExpressions
+            ).WithTriviaFrom(node);
+        }
+
         private ExpressionSyntax ReplaceVariableWithCast(ExpressionSyntax expression, DeclarationPatternSyntax declaration, ExpressionSyntax governingExpression)
         {
             if (declaration.Designation is SingleVariableDesignationSyntax variableDesignation)

tests/EntityFrameworkCore.Projectables.Generator.Tests/ProjectionExpressionGeneratorTests.DictionaryIndexInitializer_IsBeingRewritten.verified.txt

@@ -0,0 +1,29 @@
+// <auto-generated/>
+#nullable disable
+using System;
+using System.Linq;
+using System.Collections.Generic;
+using EntityFrameworkCore.Projectables;
+using Foo;
+
+namespace EntityFrameworkCore.Projectables.Generated
+{
+    [global::System.ComponentModel.EditorBrowsable(global::System.ComponentModel.EditorBrowsableState.Never)]
+    static class Foo_EntityExtensions_ToDictionary
+    {
+        static global::System.Linq.Expressions.Expression<global::System.Func<global::Foo.EntityExtensions.Entity, global::System.Collections.Generic.Dictionary<string, object>>> Expression()
+        {
+            return (global::Foo.EntityExtensions.Entity entity) => new Dictionary<string, object>
+            {
+                {
+                    "FullName",
+                    entity.FullName ?? "N/A"
+                },
+                {
+                    "Id",
+                    entity.Id.ToString()
+                }
+            };
+        }
+    }
+}

tests/EntityFrameworkCore.Projectables.Generator.Tests/ProjectionExpressionGeneratorTests.DictionaryObjectInitializer_PreservesCollectionInitializerSyntax.verified.txt

@@ -0,0 +1,25 @@
+// <auto-generated/>
+#nullable disable
+using System;
+using System.Linq;
+using System.Collections.Generic;
+using EntityFrameworkCore.Projectables;
+using Foo;
+
+namespace EntityFrameworkCore.Projectables.Generated
+{
+    [global::System.ComponentModel.EditorBrowsable(global::System.ComponentModel.EditorBrowsableState.Never)]
+    static class Foo_EntityExtensions_ToDictionary
+    {
+        static global::System.Linq.Expressions.Expression<global::System.Func<global::Foo.EntityExtensions.Entity, global::System.Collections.Generic.Dictionary<string, string>>> Expression()
+        {
+            return (global::Foo.EntityExtensions.Entity entity) => new Dictionary<string, string>
+            {
+                {
+                    "FullName",
+                    entity.FullName ?? "N/A"
+                }
+            };
+        }
+    }
+}

tests/EntityFrameworkCore.Projectables.Generator.Tests/ProjectionExpressionGeneratorTests.cs

@@ -1901,6 +1901,81 @@ public Task GenericTypesWithConstraints()
 
             return Verifier.Verify(result.GeneratedTrees[0].ToString());
         }
+
+        [Fact]
+        public Task DictionaryIndexInitializer_IsBeingRewritten()
+        {
+            // lang=csharp
+            var compilation = CreateCompilation(@"
+using System;
+using System.Linq;
+using System.Collections.Generic;
+using EntityFrameworkCore.Projectables;
+
+namespace Foo {
+    public static class EntityExtensions
+    {
+        public record Entity
+        {
+            public int Id { get; set; }
+            public string? FullName { get; set; }
+        }
+
+        [Projectable(NullConditionalRewriteSupport = NullConditionalRewriteSupport.Rewrite)]
+        public static Dictionary<string, object> ToDictionary(this Entity entity)
+            => new Dictionary<string, object> 
+            {
+                [""FullName""] = entity.FullName ?? ""N/A"",
+                [""Id""] = entity.Id.ToString(),
+            };
+    }
+}
+");
+
+            var result = RunGenerator(compilation);
+
+            Assert.Empty(result.Diagnostics);
+            Assert.Single(result.GeneratedTrees);
+
+            return Verifier.Verify(result.GeneratedTrees[0].ToString());
+        }
+
+        [Fact]
+        public Task DictionaryObjectInitializer_PreservesCollectionInitializerSyntax()
+        {
+            // lang=csharp
+            var compilation = CreateCompilation(@"
+using System;
+using System.Linq;
+using System.Collections.Generic;
+using EntityFrameworkCore.Projectables;
+
+namespace Foo {
+    public static class EntityExtensions
+    {
+        public record Entity
+        {
+            public int Id { get; set; }
+            public string? FullName { get; set; }
+        }
+
+        [Projectable(NullConditionalRewriteSupport = NullConditionalRewriteSupport.Rewrite)]
+        public static Dictionary<string, string> ToDictionary(this Entity entity)
+            => new Dictionary<string, string> 
+            {
+                { ""FullName"", entity.FullName ?? ""N/A"" }
+            };
+    }
+}
+");
+
+            var result = RunGenerator(compilation);
+
+            Assert.Empty(result.Diagnostics);
+            Assert.Single(result.GeneratedTrees);
+
+            return Verifier.Verify(result.GeneratedTrees[0].ToString());
+        }
 
         #region Helpers