[2.0.0-preview1] Design: Stop invoking Startup.ConfigureServices

[bricelam]

Part of #8164

Note, this removes to following closure of dependencies form EFCore.Design.

• System.Globalization.Extensions
• System.Net.WebSockets
• System.Reflection.TypeExtensions
• System.Security.Claims
• System.Security.Principal
• System.Text.Encodings.Web
• Microsoft.AspNetCore.Hosting.Abstractions
• Microsoft.AspNetCore.Hosting.Server.Abstractions
• Microsoft.AspNetCore.Http.Abstractions
• Microsoft.AspNetCore.Http.Features
• Microsoft.Extensions.FileProviders.Abstractions
• Microsoft.Extensions.Hosting.Abstractions

Providers: If you're not already implementing IDesignTimeServices in the type pointed to by [DesignTimeProviderServices], you'll need to after this.

[smitpatel]

Correct base branch?

[bricelam]

@smitpatel Yes, but only for review... 😉 It's based on #8314

[ajcvickers]

This looks good to me. Much better than what we had. Two things:

• What exception message does the user get if they still have the old-style ConfigureServices app?
• I still think that given how clean the context factory in the template looks to me, that if Damian is okay with it, then we should only support the context factory going forward. It is very self-documenting and very un-magic.

[bricelam]

What exception message does the user get if they still have the old-style ConfigureServices app?

Most will get the typical error:

No parameterless constructor was found on 'ApplicationDbContext'. Either add a parameterless constructor to 'ApplicationDbContext' or add an implementation of 'IDbContextFactory<ApplicationDbContext>' in the same assembly as 'ApplicationDbContext'.

There is a corner case that can happen on the first Add-Migration when your context has been added to the application services, but isn't in either the startup or target project. These advanced users will receive a no context/can't find context error, but the solution is the same--add an IDbContextFactory.

[ajcvickers]

@bricelam Think we need a better message that indicates that this has happened not because they did something "wrong" but because we have made a change in how things work in 2.0. Probably with a fwlink to docs on how to convert. But happy for all this to happen later.