RC1: UnreachableException when loading with proxies and a JSON-mapped complex property

[ajcvickers]

Minimal repro:

await using var context = new BlogsContext();
await context.Database.EnsureDeletedAsync();
await context.Database.EnsureCreatedAsync();
await context.Seed();

context.ChangeTracker.Clear();

var blogs = await context.Blogs.ToListAsync();
context.Entry(blogs[0]).Collection(e => e.Posts).Load();

public class Blog
{
    public int Id { get; private set; }
    public string Name { get; set; } = null!;
    public virtual List<Post> Posts { get; } = new();
}

public class Post
{
    public int Id { get; private set; }
    public string Title { get; set; } = null!;
    public int BlogId { get; set; }
    public virtual Blog Blog { get; set; } = null!;
    public PostMetadata? Metadata { get; set; }
}

public class PostMetadata
{
    public int Views { get; set; }
}

public class BlogsContext : DbContext
{
    public DbSet<Blog> Blogs
        => Set<Blog>();

    public DbSet<Post> Posts
        => Set<Post>();

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        => optionsBuilder
            .UseSqlServer(@"Data Source=(LocalDb)\MSSQLLocalDB;Database=AllTogetherNow")
            .UseLazyLoadingProxies()
            .LogTo(Console.WriteLine, LogLevel.Information)
            .EnableSensitiveDataLogging();

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Post>().OwnsOne(
            post => post.Metadata, ownedNavigationBuilder =>
            {
                ownedNavigationBuilder.ToJson();
            });

        base.OnModelCreating(modelBuilder);
    }

    public async Task Seed()
    {
        var blogs = new List<Blog>
        {
            new()
            {
                Name = ".NET Blog",
                Posts =
                {
                    new() { Title = "Productivity comes to .NET MAUI in Visual Studio 2022" },
                    new() { Title = "Announcing .NET 7 Preview 7" },
                    new() { Title = "ASP.NET Core updates in .NET 7 Preview 7" },
                    new() { Title = "Announcing Entity Framework 7 Preview 7: Interceptors!" }
                }
            },
            new()
            {
                Name = "1unicorn2",
                Posts =
                {
                    new() { Title = "Hacking my Sixth Form College network in 1991" },
                    new() { Title = "All your versions are belong to us" },
                    new() { Title = "Moving to Linux" },
                    new() { Title = "Welcome to One Unicorn 2.0!" }
                }
            }
        };

        await AddRangeAsync(blogs);
        await SaveChangesAsync();
    }
}

Exception:

Unhandled exception. System.Diagnostics.UnreachableException: The program executed an instruction that was thought to be unreachable.
   at Microsoft.EntityFrameworkCore.Query.RelationalShapedQueryCompilingExpressionVisitor.ShaperProcessingExpressionVisitor.JsonEntityMaterializerRewriter.VisitSwitch(SwitchExpression switchExpression)
   at System.Linq.Expressions.ExpressionVisitor.VisitBinary(BinaryExpression node)
   at System.Dynamic.Utils.ExpressionVisitorUtils.VisitBlockExpressions(ExpressionVisitor visitor, BlockExpression block)
   at System.Linq.Expressions.ExpressionVisitor.VisitBlock(BlockExpression node)
   at System.Linq.Expressions.ExpressionVisitor.VisitConditional(ConditionalExpression node)
   at Microsoft.EntityFrameworkCore.Query.RelationalShapedQueryCompilingExpressionVisitor.ShaperProcessingExpressionVisitor.JsonEntityMaterializerRewriter.VisitConditional(ConditionalExpression conditionalExpression)
   at System.Linq.Expressions.ExpressionVisitor.VisitConditional(ConditionalExpression node)
   at Microsoft.EntityFrameworkCore.Query.RelationalShapedQueryCompilingExpressionVisitor.ShaperProcessingExpressionVisitor.JsonEntityMaterializerRewriter.VisitConditional(ConditionalExpression conditionalExpression)
   at System.Dynamic.Utils.ExpressionVisitorUtils.VisitBlockExpressions(ExpressionVisitor visitor, BlockExpression block)
   at System.Linq.Expressions.ExpressionVisitor.VisitBlock(BlockExpression node)
   at Microsoft.EntityFrameworkCore.Query.RelationalShapedQueryCompilingExpressionVisitor.ShaperProcessingExpressionVisitor.JsonEntityMaterializerRewriter.Rewrite(BlockExpression jsonEntityShaperMaterializer)
   at Microsoft.EntityFrameworkCore.Query.RelationalShapedQueryCompilingExpressionVisitor.ShaperProcessingExpressionVisitor.CreateJsonShapers(IEntityType entityType, Boolean nullable, ParameterExpression jsonReaderDataParameter, ParameterExpression keyValuesParameter, Expression parentEntityExpression, INavigation navigation)
   at Microsoft.EntityFrameworkCore.Query.RelationalShapedQueryCompilingExpressionVisitor.ShaperProcessingExpressionVisitor.VisitExtension(Expression extensionExpression)
   at Microsoft.EntityFrameworkCore.Query.RelationalShapedQueryCompilingExpressionVisitor.ShaperProcessingExpressionVisitor.ProcessShaper(Expression shaperExpression, RelationalCommandCache& relationalCommandCache, IReadOnlyList`1& readerColumns, LambdaExpression& relatedDataLoaders, Int32& collectionId)       
   at Microsoft.EntityFrameworkCore.Query.RelationalShapedQueryCompilingExpressionVisitor.VisitShapedQuery(ShapedQueryExpression shapedQueryExpression)
   at Microsoft.EntityFrameworkCore.Query.ShapedQueryCompilingExpressionVisitor.VisitExtension(Expression extensionExpression)
   at Microsoft.EntityFrameworkCore.Query.RelationalShapedQueryCompilingExpressionVisitor.VisitExtension(Expression extensionExpression)
   at Microsoft.EntityFrameworkCore.Query.QueryCompilationContext.CreateQueryExecutor[TResult](Expression query)
   at Microsoft.EntityFrameworkCore.Storage.Database.CompileQuery[TResult](Expression query, Boolean async)
   at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.CompileQueryCore[TResult](IDatabase database, Expression query, IModel model, Boolean async)
   at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.<>c__DisplayClass9_0`1.<Execute>b__0()
   at Microsoft.EntityFrameworkCore.Query.Internal.CompiledQueryCache.GetOrAddQuery[TResult](Object cacheKey, Func`1 compiler)
   at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.Execute[TResult](Expression query)
   at Microsoft.EntityFrameworkCore.Query.Internal.EntityQueryProvider.Execute[TResult](Expression expression)
   at Microsoft.EntityFrameworkCore.Query.Internal.EntityQueryable`1.GetEnumerator()
   at Microsoft.EntityFrameworkCore.EntityFrameworkQueryableExtensions.Load[TSource](IQueryable`1 source)
   at Microsoft.EntityFrameworkCore.Internal.EntityFinder`1.Load(INavigation navigation, InternalEntityEntry entry, LoadOptions options)
   at Microsoft.EntityFrameworkCore.Internal.EntityFinderCollectionLoaderAdapter.Load(InternalEntityEntry entry, LoadOptions options)
   at Microsoft.EntityFrameworkCore.ChangeTracking.CollectionEntry.Load(LoadOptions options)
   at Microsoft.EntityFrameworkCore.ChangeTracking.CollectionEntry.Load()
   at Program.<Main>$(String[] args) in C:\local\code\AllTogetherNow\Daily\Daily.cs:line 15
   at Program.<Main>$(String[] args) in C:\local\code\AllTogetherNow\Daily\Daily.cs:line 15
   at Program.<Main>(String[] args)

[ajcvickers]

/cc @maumar

[maumar]

when processing entity materialization code, adapting it for JSON, we assume the entity type can be a result of BlockExpression (normal case) or a NewExpression (when the ctor is the only thing and we don't need to do any other assignments). However, for proxies, the block is wrapped around Convert node, since the instance generated of of Proxy type, but we expect the actual type there.