Error when same C type is imported twice and the type is extended by one of the modules

[vinocher-bc]

Description

The attached test imports two C modules, both of which define the same C type (enum __x_ABI_CWindows_CGraphics_CImaging_CBitmapPixelFormat). One of the modules extends that type, but the other does not. A compiler error occurs when the extended type is accessed, presumably because the compiler doesn't recognize the existence of the extension.

Build the attached minimal repro sample:
cmake -S . -B build -G Ninja
cmake --build build

A compiler error occurs, which should not:

main.swift:11:42: error: type 'BitmapPixelFormat' (aka '__x_ABI_CWindows_CGraphics_CImaging_CBitmapPixelFormat') has no member 'bgra8'

Reproduction

Repro: swiftImportTest.zip

Excerpts:
C Type being imported using InteropTest and InteropTest2 modules:

enum __x_ABI_CWindows_CGraphics_CImaging_CBitmapPixelFormat
{
:
    __x_ABI_CWindows_CGraphics_CImaging_CBitmapPixelFormat_Bgra8 = 87,
:
};

ModuleTest extends the C type:

import InteropTest

public typealias BitmapPixelFormat = __x_ABI_CWindows_CGraphics_CImaging_CBitmapPixelFormat

extension ModuleTest.BitmapPixelFormat {
    public static var bgra8 : ModuleTest.BitmapPixelFormat {
        __x_ABI_CWindows_CGraphics_CImaging_CBitmapPixelFormat_Bgra8
    }
}

ModuleTest2 does not extend the C type:

import InteropTest2

Use of type:

import ModuleTest
import ModuleTest2

func main() {
    // Compile error: type 'BitmapPixelFormat' (aka '__x_ABI_CWindows_CGraphics_CImaging_CBitmapPixelFormat') has no member 'bgra8'
    let y = ModuleTest.BitmapPixelFormat.bgra8
    print("Format: \(y)")
}   

Expected behavior

This code should compile successfully.

Environment

compnerd.org Swift version 6.0-dev (LLVM a527f49f462b0d7, Swift eef85a7)
Target: x86_64-unknown-windows-msvc

Additional information

No response