Fix struct complex type boxing in collection materialization (#37934)

Fixes #37926

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: roji

src/EFCore.Relational/Query/RelationalShapedQueryCompilingExpressionVisitor.ShaperProcessingExpressionVisitor.cs

@@ -1479,7 +1479,13 @@ Expression CompensateForCollectionMaterialization(ParameterExpression parameter,
             {
                 if (_containsCollectionMaterialization)
                 {
-                    _valuesArrayInitializers!.Add(parameter);
+                    var expressionToAdd = (Expression)parameter;
+                    if (expressionToAdd.Type.IsValueType)
+                    {
+                        expressionToAdd = Convert(expressionToAdd, typeof(object));
+                    }
+
+                    _valuesArrayInitializers!.Add(expressionToAdd);
                     return Convert(
                         ArrayIndex(
                             _valuesArrayExpression!,

test/EFCore.Cosmos.FunctionalTests/Query/Associations/ComplexProperties/ComplexPropertiesCollectionCosmosTest.cs

@@ -221,6 +221,10 @@ FROM root c
     }
 
 
+    // Cosmos doesn't support entity collection navigations across documents
+    public override Task Project_struct_complex_type_with_entity_collection_navigation()
+        => Task.CompletedTask;
+
     [ConditionalFact]
     public virtual void Check_all_tests_overridden()
         => TestHelpers.AssertAllMethodsOverridden(GetType());

test/EFCore.Specification.Tests/Query/Associations/ComplexProperties/ComplexPropertiesCollectionTestBase.cs

@@ -5,4 +5,70 @@ namespace Microsoft.EntityFrameworkCore.Query.Associations.ComplexProperties;
 
 public abstract class ComplexPropertiesCollectionTestBase<TFixture>(TFixture fixture)
     : AssociationsCollectionTestBase<TFixture>(fixture)
-    where TFixture : ComplexPropertiesFixtureBase, new();
+    where TFixture : ComplexPropertiesFixtureBase, new()
+{
+    #region 37926
+
+    [ConditionalFact]
+    public virtual async Task Project_struct_complex_type_with_entity_collection_navigation()
+    {
+        var contextFactory = await InitializeNonSharedTest<Context37926>(
+            seed: async context =>
+            {
+                context.Add(new Context37926.Parent
+                {
+                    Id = 1,
+                    Coords = new Context37926.Coords { X = 1, Y = 2 },
+                    Children = [new() { Id = 1, Name = "Child1" }]
+                });
+                await context.SaveChangesAsync();
+            });
+
+        await using var context = contextFactory.CreateDbContext();
+
+        var result = await context.Set<Context37926.Parent>()
+            .OrderBy(p => p.Id)
+            .Select(p => new { p.Coords, p.Children })
+            .FirstAsync();
+
+        Assert.Equal(1, result.Coords.X);
+        Assert.Single(result.Children);
+    }
+
+    protected class Context37926(DbContextOptions options) : DbContext(options)
+    {
+        protected override void OnModelCreating(ModelBuilder modelBuilder)
+        {
+            modelBuilder.Entity<Parent>(b =>
+            {
+                b.Property(e => e.Id).ValueGeneratedNever();
+                b.ComplexProperty(e => e.Coords);
+                b.HasMany(e => e.Children).WithOne().HasForeignKey(c => c.ParentId);
+            });
+
+            modelBuilder.Entity<Child>().Property(e => e.Id).ValueGeneratedNever();
+        }
+
+        public class Parent
+        {
+            public int Id { get; set; }
+            public Coords Coords { get; set; }
+            public List<Child> Children { get; set; } = [];
+        }
+
+        public struct Coords
+        {
+            public int X { get; set; }
+            public int Y { get; set; }
+        }
+
+        public class Child
+        {
+            public int Id { get; set; }
+            public required string Name { get; set; }
+            public int ParentId { get; set; }
+        }
+    }
+
+    #endregion 37926
+}

test/EFCore.SqlServer.FunctionalTests/Query/Associations/ComplexJson/ComplexJsonCollectionSqlServerTest.cs

@@ -352,6 +352,23 @@ FROM [RootEntity] AS [r]
         }
     }
 
+    public override async Task Project_struct_complex_type_with_entity_collection_navigation()
+    {
+        await base.Project_struct_complex_type_with_entity_collection_navigation();
+
+        AssertSql(
+            """
+SELECT [p0].[Coords_X], [p0].[Coords_Y], [p0].[Id], [c].[Id], [c].[Name], [c].[ParentId]
+FROM (
+    SELECT TOP(1) [p].[Coords_X], [p].[Coords_Y], [p].[Id]
+    FROM [Parent] AS [p]
+    ORDER BY [p].[Id]
+) AS [p0]
+LEFT JOIN [Child] AS [c] ON [p0].[Id] = [c].[ParentId]
+ORDER BY [p0].[Id]
+""");
+    }
+
     [ConditionalFact]
     public virtual void Check_all_tests_overridden()
         => TestHelpers.AssertAllMethodsOverridden(GetType());