Generating migrations for entities without a namespace produces an empty using statement

[armanossiloko]

After creating a DbContext and an entity within the Program.cs file, calling add-migration produces a migration file with syntax error:

The produced migration looks like this and everything is okay in it (it was generated correctly) except for line 1 where it has an empty using:

using ;
using Microsoft.EntityFrameworkCore.Migrations;
using Npgsql.EntityFrameworkCore.PostgreSQL.Metadata;
#nullable disable
namespace WebApplication1.Migrations
{
    /// <inheritdoc />
    public partial class test : Migration
    {
        // protected override void Up() omitted for brevity

        // protected override void Down() omitted for brevity
    }
}

Program.cs:

```csharp
using Microsoft.EntityFrameworkCore;
using Npgsql;

var builder = WebApplication.CreateBuilder(args);
var dataSource = new NpgsqlDataSourceBuilder(builder.Configuration.GetConnectionString("Database"))
    .EnableDynamicJson().Build();
builder.Services.AddDbContext<MyDbContext>(options => options.UseNpgsql(dataSource));

var app = builder.Build();
//app.MapGet("/", (MyDbContext context) => ...
//app.MapGet("/add", (MyDbContext context) => ...
//app.MapGet("/update", (MyDbContext context) => ...
app.Run();

public class Person
{
    public int Id { get; set; }
    public required string Name { get; set; }
    public List<Address> Addresses { get; set; } = [];
}
public class Address
{
    public int Id { get; set; }
    public int PersonId { get; set; }
    public virtual Person? Person { get; set; }
    public Metadata Metadata { get; set; }
}
public class Metadata
{
    public int Age { get; set; }
    public string? Interest { get; set; }
}

public class MyDbContext(DbContextOptions<MyDbContext> options) : DbContext(options)
{
    public DbSet<Person> People { get; set; }
    public DbSet<Address> Addresses { get; set; }
    protected override void OnModelCreating(ModelBuilder builder)
    {
        base.OnModelCreating(builder);
        builder.Entity<Address>()
            .Property(e => e.Metadata)
            .HasColumnType("jsonb");
    }
}

The project file:

<Project Sdk="Microsoft.NET.Sdk.Web">

	<PropertyGroup>
		<TargetFramework>net8.0</TargetFramework>
		<Nullable>enable</Nullable>
		<ImplicitUsings>enable</ImplicitUsings>
	</PropertyGroup>

	<ItemGroup>
		<PackageReference Include="Microsoft.EntityFrameworkCore.Design" Version="8.0.10">
			<PrivateAssets>all</PrivateAssets>
			<IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
		</PackageReference>
		<PackageReference Include="Microsoft.EntityFrameworkCore.Relational" Version="8.0.10" />
		<PackageReference Include="Microsoft.EntityFrameworkCore.Tools" Version="8.0.10">
			<PrivateAssets>all</PrivateAssets>
			<IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
		</PackageReference>
		<PackageReference Include="Npgsql.EntityFrameworkCore.PostgreSQL" Version="8.0.8" />
	</ItemGroup>

</Project>

[roji]

Confirmed, minimal repro:

var context = new MyDbContext();

public class Address
{
    public int Id { get; set; }
    public int PersonId { get; set; }
    public Metadata Metadata { get; set; }
}

public class Metadata
{
    public int Age { get; set; }
    public string? Interest { get; set; }
}

public class MyDbContext : DbContext
{
    public DbSet<Address> Addresses { get; set; }

    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        => optionsBuilder.UseNpgsql("Host=localhost;Username=test;Password=test");

    protected override void OnModelCreating(ModelBuilder builder)
    {
        builder.Entity<Address>()
            .Property(e => e.Metadata)
            .HasColumnType("jsonb");
    }
}