Generic result builder "buildExpression" inference bug

[stephencelis]

Describe the bug

A generic result builder with a buildExpression that locks uses these generics must still constrain the buildBlock against those same generics when it reaches a certain complexity.

To Reproduce

I've tried to create a minimal repro, though it may minimize a little further.

protocol P0<A0, A1> {
  associatedtype A0
  associatedtype A1
  func f(_ a0: A0, _ a1: A1)
}

struct S0<A0, A1>: P0 {
  func f(_ a0: A0, _ a1: A1) {}
}

@resultBuilder
enum B<A0, A1> {
  static func buildExpression<T: P0<A0, A1>>(_ expression: T) -> T { expression }

  static func buildPartialBlock<R>(first: R) -> R { first }

  static func buildPartialBlock<R0: P0, R1: P0<R0.A0, R0.A1>>(
    accumulated: R0, next: R1
  ) -> some P0<R0.A0, R0.A1>
  // Commenting the next line in gets things building,
  // even though it should be inferred via 'buildExpression'
//  where R0.A0 == A0, R1.A1 == A1
  {
    accumulated
  }
}

struct S1<B0> {}
enum E1<B0, B1> {}

protocol P1 {
  associatedtype B0
  var s1: S1<B0> { get set }
}

protocol P2 {
  associatedtype B0
  associatedtype B1
  static func e1(_: E1<B0, B1>) -> Self
}

extension P0
where
  A0: P1,
  A1: P2,
  A0.B0 == A1.B0
{
  func g<GReturnValue: P0>(
    @B<GReturnValue.A0, GReturnValue.A1> build: () -> GReturnValue
  ) -> some P0<A0, A1>
  where
    GReturnValue.A0 == A0.B0,
    GReturnValue.A1 == A1.B1
  {
    S0()
  }
}

struct S2: P0 {
  struct A0: P1 {
    var s1: S1<T0>
  }
  enum A1: P2 {
    case e1(E1<T0, T1>)
  }

  struct T0 {}
  enum T1 {}

  func f(_ a0: A0, _ a1: A1) {}
}

@B<S2.A0, S2.A1>
var p: some P0<S2.A0, S2.A1> {
  S0<S2.A0, S2.A1>()
    .g { // error: Generic parameter 'GReturnValue' could not be inferred
      S0<S2.T0, S2.T1>()
      S0<S2.T0, S2.T1>()
    }
}

Expected behavior

I expect the above to build without specifying the generic constraints on buildPartialBlock(accumulated:next:).

Environment (please complete the following information):

• Xcode 14 (Swift 5.7 Development Snapshot 2022-06-13 (a))