Make DelegateEndpointConventionBuilder constructors public

[captainsafia]

Background and Motivation

For .NET 6, we added support for OpenAPI extension methods on the DelegateEndpointConventionBuilder used in minimal apps. The DelegateEndpointConventionBuilder is currently implemented as a public sealed class with internal constructors.

While debugging a scenario, we realized that this posed a problem for scenarios where developers wanted to use the extension methods on a builder returned from a 3rd-party API or external source.

// Some library code
public static DelegateEndpointConventionBuilder MapMyFrameworkMethods()
{
...
}

// Some user code that is not possible
app.MapMyFrameworkMethods().ExcludeFromDescription();

Proposed API

namespace Microsoft.AspNetCore.Builder
{
  public class DelegateEndpointConventionBuilder
  {
-    internal DelegateEndpointConventionBuilder(List<IEndpointConventionBuilder> endpointConventionBuilders)
+    public DelegateEndpointConventionBuilder(List<IEndpointConventionBuilder> endpointConventionBuilders)
}

Usage Examples

public static DelegateEndpointConventionBuilder MapToDos(this IEndpointRouteBuilder endpointRouteBuilder)
{
  List<IEndpointConventionBuilder> builders = new();
  builders.Add(endpointRouteBuilder.MapPost("/create", () => { ... });
  builders.Add(endpointRouteBuilder.MapGet("/all", () => { ... });
  return new DelegateEndpointConventionBuilder(builders);
}

app.MapToDos().ExcludeFromDescription();

Alternative Designs

One alternative is to have the extension methods target IEndpointConventionBuilder instead of DelegateEndpointConventionBuilder but this presents some problems because:

• The compiler will fail to resolve generic types correctly for extension methods that implement more than one generic Produces<TResponse>(TBuilder)
• We want to keep the high level of specificity for what builders this extension method targets

Risks

• The DelegateEndpointConventionBuilder was introduced in .NET 6 so this is not a breaking change.
• Unlike other IEndpointConventionBuilders the DelegateEndpointConventionBuilder has a requirement for this type of extensibility so it's the only one that follows the pattern of public class and public constructor.

[ghost]

Thank you for your API proposal. I'm removing the api-ready-for-review label. API Proposals should be submitted for review through Issues based on this template.

[captainsafia]

@dotnet/aspnet-build Can I get help merging?

The Linux helix run has passed for this but the other legs are stuck: https://helix.dot.net/api/jobs/cfb0e973-8053-41c1-a5be-8e37deee1a86/workitems?api-version=2019-06-17

Edit: Actually looks like all the Helix legs passed successfully

[dougbu]

Do not merge this as-is

[dougbu]

See

Detected modification to baseline API files. PublicAPI.Shipped.txt files should only be updated

The Shipped files should never change except immediately after an RTM release e.g. 6.0.0. In between, change PublicAPI.Unshipped.txt files. Add *Removed* lines if necessary to effectively override something that has shipped but carefully.

[dougbu]

Put another way: Unless this was in 5.0.0, the method hasn't shipped.