[C++ interop] Swift overload mysteriously not found when using imported namespaced enum

[AnthonyLatsis]

Description

No response

Reproduction

// RUN: %empty-directory(%t)
// RUN: %empty-directory(%t/include)
// RUN: split-file %s %t
//
// RUN: %target-swift-frontend -emit-module -module-name a -emit-module-path %t/include/a.swiftmodule %t/a.swift -cxx-interoperability-mode=default -I %t/include
// RUN: %target-swift-frontend -typecheck -primary-file %t/b1.swift %t/b2.swift -cxx-interoperability-mode=default -I %t/include

//--- include/module.modulemap
module cxx {
  header "header.h"
  export *
}

//--- include/header.h
namespace swift {
enum class DiagID {
  x, y, z
};
}

//--- a.swift
import cxx
public struct Loc1 {}
public struct Loc2 {}
public struct Engine {
  public func diagnose(_: swift.DiagID, _: Loc1) {}
  public func diagnose(_: swift.DiagID, _: Loc2) {}
}

//--- b1.swift
import a
import cxx
private func test1(engine: Engine, loc: Loc1) {
  engine.diagnose(.y, loc)
}

//--- b2.swift
import a
import cxx
private func test2(engine: Engine, loc: Loc2, id: swift.DiagID) {
  engine.diagnose(id, loc)
}

/Users/alatsis/Desktop/swiftlang/build/Ninja-RelWithDebInfoAssert/swift-macosx-arm64/test-macosx-arm64/Interop/Cxx/Output/bug.swift.tmp/b1.swift:4:23: error: cannot convert value of type 'Loc1' to expected argument type 'Loc2'
2 | import cxx
3 | private func test1(engine: Engine, loc: Loc1) {
4 |   engine.diagnose(.y, loc)
  |                       `- error: cannot convert value of type 'Loc1' to expected argument type 'Loc2'
5 | }
6 | 

Expected behavior

Success.

Environment

Swift version 6.2-dev (LLVM 8bcf2671393ccfb, Swift 8acde34)

Additional information

No response

[AnthonyLatsis]

Reduced from:

// RUN: %empty-directory(%t)
// RUN: %empty-directory(%t/include)
// RUN: split-file %s %t
//
// RUN: %target-swift-frontend -emit-module -module-name a -emit-module-path %t/include/a.swiftmodule %t/a.swift -cxx-interoperability-mode=default -I %t/include
// RUN: %target-swift-frontend -emit-module -module-name b -emit-module-path %t/include/b.swiftmodule %t/b.swift -cxx-interoperability-mode=default -I %t/include
// RUN: %target-swift-frontend -typecheck -primary-file %t/c1.swift %t/c2.swift -cxx-interoperability-mode=default -I %t/include

//--- include/module.modulemap
module cxx {
  header "header.h"
  export *
}

//--- include/header.h
namespace swift {
enum class DiagID {
  x, y, z
};
}

//--- a.swift
import cxx
public struct Loc1 {}
public protocol DiagArgument {}
public struct Engine {
  public func diagnose(_: swift.DiagID, _: [DiagArgument], at: Loc1?) {}
  public func diagnose(_: swift.DiagID, _: DiagArgument...,at: Loc1?) {}
}

//--- b.swift
import a
import cxx
public struct Loc2 {}
extension Engine {
  public func diagnose(_: swift.DiagID, _: DiagArgument...,at: Loc2) {}
  public func diagnose(_: swift.DiagID, _: [DiagArgument], at: Loc2) {}
}

//--- c1.swift
import a
import b
import cxx
private func foo1(engine: Engine, loc: Loc1?) {
  engine.diagnose(.y, [], at: loc)
}

//--- c2.swift
import a
import cxx
private func foo2(engine: Engine, id: swift.DiagID, args: DiagArgument..., loc: Loc1?) {
  engine.diagnose(id, args, at: loc)
}