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

[ahoppen]

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.

[compnerd]

It might be worth considering adding -visualc-tools-version and -windows-sdk-version flags to the invocation instead. That would save you the time and retain the ability to run the VSCode extension tests.