Windows GitHub Action runners failing with `could not build module 'ucrt'`

リンクされている GitHub Actions の実行と、swiftlang/github-workflows にある Windows ワークフロー定義から始めます。記載されている Swift バージョン全体で ucrt および _visualc_intrinsics モジュールの失敗を再現し、Docker の回避策と比較します。Docker を必要とせずに Windows actions が正常に実行され、コンテナ内でテストできないリポジトリも含まれる状態を完了とします。

The Windows GitHub actions on swift-format are failing with the following error (on 6.0, nightly, nightly-6.1). I think GitHub recently updated their Windows runners. Eg. https://github.com/swiftlang/swift-format/actions/runs/13572154457/job/38021583870

C:\Users\runneradmin\AppData\Local\Programs\Swift\Platforms\6.0.2\Windows.platform\Developer\SDKs\Windows.sdk\usr\lib\swift\shims/LibcOverlayShims.h:27:10: note: while building module 'ucrt' imported from C:\Users\runneradmin\AppData\Local\Programs\Swift\Platforms\6.0.2\Windows.platform\Developer\SDKs\Windows.sdk\usr\lib\swift\shims/LibcOverlayShims.h:27:
 25 | #endif
 26 | #if defined(_WIN32) && !defined(__CYGWIN__)
 27 | #include <errno.h>
    |          `- note: while building module 'ucrt' imported from C:\Users\runneradmin\AppData\Local\Programs\Swift\Platforms\6.0.2\Windows.platform\Developer\SDKs\Windows.sdk\usr\lib\swift\shims/LibcOverlayShims.h:27:
 28 | #include <io.h>
 30 | #if defined(__clang__) && (defined(_M_ARM64) || defined(_M_ARM64EC))
 31 | #include <arm_neon.h>
C:\Program Files\Microsoft Visual Studio\2022\Enterprise\VC\Tools\MSVC\14.43.34808\include\intrin.h:35:18: error: could not build module '_visualc_intrinsics'
  33 | 
  34 |     #if (defined (_M_IX86) || defined (_M_X64) || (defined(_M_ARM64) && defined(USE_SOFT_INTRINSICS))) && !defined(_CHPE_ONLY_) && (!defined(_M_ARM64EC) || !defined(_DISABLE_SOFTINTRIN_))
  35 |         #include <immintrin.h>
     |                  `- error: could not build module '_visualc_intrinsics'
  36 |         #include <ammintrin.h>
  37 |     #endif
<module-includes>:1:10: note: in file included from <module-includes>:1:
1 | #include "LibcOverlayShims.h"
  |          `- note: in file included from <module-includes>:1:
2 | 
<unknown>:0: error: could not build C module 'SwiftOverlayShims'
C:\Users\runneradmin\AppData\Local\Programs\Swift\Platforms\6.0.2\Windows.platform\Developer\SDKs\Windows.sdk\usr\lib\swift\shims/LibcOverlayShims.h:27:10: error: could not build module 'ucrt'
 25 | #endif
 26 | #if defined(_WIN32) && !defined(__CYGWIN__)
 27 | #include <errno.h>
    |          `- error: could not build module 'ucrt'
 28 | #include <io.h>
 29 | typedef int mode_t;

I was able to work around this by running tests inside Docker container on Windows again but that adds 5-10 minutes to CI time and eg. the VS Code extension repo can’t run their tests inside a Docker container.