Fix implicit new() expression not generating valid code in Projectables

Author: Copilot

src/EntityFrameworkCore.Projectables.Generator/SyntaxRewriters/ExpressionSyntaxRewriter.cs

@@ -298,6 +298,37 @@ public ExpressionSyntaxRewriter(INamedTypeSymbol targetTypeSymbol, NullCondition
         ).WithTriviaFrom(node);
     }
 
+    public override SyntaxNode? VisitImplicitObjectCreationExpression(ImplicitObjectCreationExpressionSyntax node)
+    {
+        // Target-typed new expressions (new() { ... }) are not supported in expression trees.
+        // Resolve the concrete type from the semantic model and rewrite to an explicit new T() { ... }.
+        var typeInfo = _semanticModel.GetTypeInfo(node);
+        if (typeInfo.Type is INamedTypeSymbol namedType)
+        {
+            var typeName = SyntaxFactory.ParseTypeName(
+                namedType.ToDisplayString(SymbolDisplayFormat.FullyQualifiedFormat))
+                .WithLeadingTrivia(SyntaxFactory.Space);
+
+            var visitedArgumentList = node.ArgumentList is not null
+                ? (ArgumentListSyntax?)Visit(node.ArgumentList)
+                : SyntaxFactory.ArgumentList();
+
+            var visitedInitializer = node.Initializer is not null
+                ? (InitializerExpressionSyntax?)Visit(node.Initializer)
+                : null;
+
+            return SyntaxFactory.ObjectCreationExpression(
+                node.NewKeyword,
+                typeName,
+                visitedArgumentList ?? SyntaxFactory.ArgumentList(),
+                visitedInitializer
+            ).WithLeadingTrivia(node.GetLeadingTrivia())
+             .WithTrailingTrivia(node.GetTrailingTrivia());
+        }
+
+        return base.VisitImplicitObjectCreationExpression(node);
+    }
+
     public override SyntaxNode? VisitIsPatternExpression(IsPatternExpressionSyntax node)
     {
         // Pattern matching is not supported in expression trees (CS8122).

tests/EntityFrameworkCore.Projectables.Generator.Tests/MethodTests.ImplicitNewExpression_SimpleObjectInitializer_RewritesToExplicitType.verified.txt

@@ -0,0 +1,20 @@
+// <auto-generated/>
+#nullable disable
+using EntityFrameworkCore.Projectables;
+using Foo;
+
+namespace EntityFrameworkCore.Projectables.Generated
+{
+    [global::System.ComponentModel.EditorBrowsable(global::System.ComponentModel.EditorBrowsableState.Never)]
+    static class Foo_Dest_From_P0_Foo_Source
+    {
+        static global::System.Linq.Expressions.Expression<global::System.Func<global::Foo.Source, global::Foo.Dest>> Expression()
+        {
+            return (global::Foo.Source s) => new global::Foo.Dest()
+            {
+                Name = s.Name,
+                Value = s.Value,
+            };
+        }
+    }
+}

tests/EntityFrameworkCore.Projectables.Generator.Tests/MethodTests.ImplicitNewExpression_WithTernaryAndNullConditional_RewritesToExplicitType.verified.txt

@@ -0,0 +1,21 @@
+// <auto-generated/>
+#nullable disable
+using EntityFrameworkCore.Projectables;
+using Foo;
+
+namespace EntityFrameworkCore.Projectables.Generated
+{
+    [global::System.ComponentModel.EditorBrowsable(global::System.ComponentModel.EditorBrowsableState.Never)]
+    static class Foo_Dest_From_P0_Foo_Source
+    {
+        static global::System.Linq.Expressions.Expression<global::System.Func<global::Foo.Source, global::Foo.Dest>> Expression()
+        {
+            return (global::Foo.Source s) => new global::Foo.Dest()
+            {
+                Name = s.Name,
+                Status = s.IsActive ? "Active" : "Inactive",
+                Code = s.Detail.Code,
+            };
+        }
+    }
+}

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

@@ -799,4 +799,79 @@ class Bar {
 
         return Verifier.Verify(result.GeneratedTrees[0].ToString());
     }
+
+    [Fact]
+    public Task ImplicitNewExpression_SimpleObjectInitializer_RewritesToExplicitType()
+    {
+        var compilation = CreateCompilation(@"
+using EntityFrameworkCore.Projectables;
+
+namespace Foo {
+    class Source {
+        public string Name { get; set; }
+        public int Value { get; set; }
+    }
+
+    class Dest {
+        public string Name { get; set; }
+        public int Value { get; set; }
+
+        [Projectable]
+        public static Dest From(Source s) => new()
+        {
+            Name = s.Name,
+            Value = s.Value,
+        };
+    }
+}
+");
+
+        var result = RunGenerator(compilation);
+
+        Assert.Single(result.Diagnostics.Where(d => d.Id == "EFP0012")); // factory method hint
+        Assert.Single(result.GeneratedTrees);
+
+        return Verifier.Verify(result.GeneratedTrees[0].ToString());
+    }
+
+    [Fact]
+    public Task ImplicitNewExpression_WithTernaryAndNullConditional_RewritesToExplicitType()
+    {
+        var compilation = CreateCompilation(@"
+using EntityFrameworkCore.Projectables;
+
+namespace Foo {
+    class Inner {
+        public string Code { get; set; }
+    }
+
+    class Source {
+        public string Name { get; set; }
+        public bool IsActive { get; set; }
+        public Inner Detail { get; set; }
+    }
+
+    class Dest {
+        public string Name { get; set; }
+        public string Status { get; set; }
+        public string Code { get; set; }
+
+        [Projectable(NullConditionalRewriteSupport = NullConditionalRewriteSupport.Ignore)]
+        public static Dest From(Source s) => new()
+        {
+            Name = s.Name,
+            Status = s.IsActive ? ""Active"" : ""Inactive"",
+            Code = s.Detail.Code,
+        };
+    }
+}
+");
+
+        var result = RunGenerator(compilation);
+
+        Assert.Single(result.Diagnostics.Where(d => d.Id == "EFP0012")); // factory method hint
+        Assert.Single(result.GeneratedTrees);
+
+        return Verifier.Verify(result.GeneratedTrees[0].ToString());
+    }
 }