Fix Windows unittest CI: force CPU-only build (CUDA 13.2 toolkit on runner breaks _portable_lib load)

.ci/scripts/setup-windows.ps1

@@ -1,5 +1,6 @@
 param (
-    [string]$editable = "false"
+    [string]$editable = "false",
+    [string]$cpuOnly = "false"
 )
 
 conda create --yes --quiet -n et python=3.12
@@ -13,6 +14,16 @@ conda activate et
 # Install test dependencies
 pip install -r .ci/docker/requirements-ci.txt
 
+# The Windows CI image ships CUDA toolkits on PATH, so install_executorch
+# (setup.py) auto-enables EXECUTORCH_BUILD_CUDA whenever the detected nvcc
+# version is in SUPPORTED_CUDA_VERSIONS. CPU-only jobs install CPU torch, so a
+# CUDA build of _portable_lib then fails to load its CUDA DLLs at import time
+# ("DLL load failed while importing _portable_lib"). Force a CPU-only build
+# when the caller asks for it.
+if ($cpuOnly -eq 'true') {
+    $env:CMAKE_ARGS = "$env:CMAKE_ARGS -DEXECUTORCH_BUILD_CUDA=OFF"
+}
+
 if ($editable -eq 'true') {
     install_executorch.bat --editable
 } else {

.ci/scripts/wheel/pre_build_script.sh

@@ -50,6 +50,15 @@ if [[ $UNAME_S == *"MINGW"* || $UNAME_S == *"MSYS"* ]]; then
     echo "Enabling symlinks on Windows"
     git config core.symlinks true
     git checkout -f HEAD
+
+    # Windows wheels are CPU-only (build-wheels-windows.yml sets
+    # with-cuda: disabled), but the Windows CI image ships a CUDA toolkit on
+    # PATH, which makes setup.py auto-enable EXECUTORCH_BUILD_CUDA. That bakes a
+    # CUDA _portable_lib into the CPU wheel, which then fails its DLL load in the
+    # smoke test ("DLL load failed while importing _portable_lib"). Force a
+    # CPU-only build.
+    export CMAKE_ARGS="${CMAKE_ARGS:-} -DEXECUTORCH_BUILD_CUDA=OFF"
+    echo "CMAKE_ARGS=${CMAKE_ARGS}" >> "${GITHUB_ENV}"
 fi
 
 # Manually install build requirements because `python setup.py bdist_wheel` does

.github/workflows/_unittest.yml

@@ -72,7 +72,7 @@ jobs:
           \$ErrorActionPreference = 'Stop'
           \$PSNativeCommandUseErrorActionPreference = \$true
 
-          .ci/scripts/setup-windows.ps1 -editable "${{ inputs.editable }}"
+          .ci/scripts/setup-windows.ps1 -editable "${{ inputs.editable }}" -cpuOnly true
           if (\$LASTEXITCODE -ne 0) {
               Write-Host "Setup failed. Exit code: \$LASTEXITCODE."
               exit \$LASTEXITCODE