Fix Python 3.15 smoke tests on Windows and Linux

numpy does not publish cp315 wheels on PyPI, so installing a freshly built
wheel under 3.15 / 3.15t falls back to the numpy sdist and tries to build it
from source. On Windows that build fails outright in the conda env (meson:
"Cython requires python3 dependency for link testing"), so the wheel is never
installed and the smoke test reports ModuleNotFoundError.

cp315 wheels for both numpy and pillow are published on download.pytorch.org
across cpu / cu126 / cu128 / cu129 / cu130 / xpu, so for 3.15 / 3.15t resolve
runtime deps from there with --pre (numpy is 2.6.0.dev0). All other Python
versions keep installing from PyPI unchanged.

Windows: applies to both the X64 and ARM64 smoke tests.
Linux: re-enables the smoke test for 3.15, which was skipped for this exact
reason, and applies the same dependency resolution.

The binary-build-matrix changes from the earlier revision of this PR are
dropped: #8427 has since enabled 3.15 / 3.15t by default for every OS and
removed the opt-in preview mechanism they were built on.

Author: atalman

.github/workflows/build_wheels_linux.yml

@@ -301,12 +301,7 @@ jobs:
           repository: ${{ inputs.repository  }}
           script: ${{ inputs.post-script }}
       - name: Smoke Test
-        # Skip the smoke test for Python 3.15 / 3.15t: the wheel builds fine, but
-        # the smoke test installs the wheel which pulls required runtime deps
-        # (e.g. pillow, a hard torchvision dependency) that have no cp315 wheels
-        # yet and fail to build from sdist. Re-enable once the ecosystem ships
-        # cp315 wheels.
-        if: ${{ inputs.run-smoke-test && ! startsWith(matrix.python_version, '3.15') }}
+        if: ${{ inputs.run-smoke-test }}
         shell: bash -l {0}
         env:
           PACKAGE_NAME: ${{ inputs.package-name }}
@@ -317,7 +312,15 @@ jobs:
           WHEEL_NAME=$(ls "${{ inputs.repository }}/dist/")
           echo "$WHEEL_NAME"
 
-          ${CONDA_RUN} pip install "${{ inputs.repository }}/dist/$WHEEL_NAME"
+          # numpy does not publish cp315 wheels on PyPI yet; they are available on
+          # download.pytorch.org as a pre-release. For 3.15 / 3.15t resolve runtime
+          # deps from there and allow pre-releases. Other versions use PyPI as before.
+          if [[ "${{ startsWith(matrix.python_version, '3.15') }}" == "true" ]]; then
+            ${CONDA_RUN} pip install --pre "${{ inputs.repository }}/dist/$WHEEL_NAME" \
+              --index-url "https://download.pytorch.org/whl/${CHANNEL}/${CU_VERSION}"
+          else
+            ${CONDA_RUN} pip install "${{ inputs.repository }}/dist/$WHEEL_NAME"
+          fi
           # Checking that we have a pinned version of torch in our dependency tree
           (
             pushd "${RUNNER_TEMP}"

.github/workflows/build_wheels_windows.yml

@@ -362,7 +362,15 @@ jobs:
           source "${BUILD_ENV_FILE}"
           WHEEL_NAME=$(ls "${{ inputs.repository }}/dist/")
           echo "$WHEEL_NAME"
-          ${CONDA_RUN} pip install "${{ inputs.repository }}/dist/$WHEEL_NAME"
+          # numpy does not publish cp315 wheels on PyPI yet; they are available on
+          # download.pytorch.org as a pre-release. For 3.15 / 3.15t resolve runtime
+          # deps from there and allow pre-releases. Other versions use PyPI as before.
+          if [[ "${{ startsWith(matrix.python_version, '3.15') }}" == "true" ]]; then
+            ${CONDA_RUN} pip install --pre "${{ inputs.repository }}/dist/$WHEEL_NAME" \
+              --index-url "https://download.pytorch.org/whl/${CHANNEL}/${CU_VERSION}"
+          else
+            ${CONDA_RUN} pip install "${{ inputs.repository }}/dist/$WHEEL_NAME"
+          fi
           if [[ ! -f "${{ inputs.repository }}"/${SMOKE_TEST_SCRIPT} ]]; then
             echo "${{ inputs.repository }}/${SMOKE_TEST_SCRIPT} not found"
             ${CONDA_RUN} "${{ inputs.repository }}/${ENV_SCRIPT}" python -c "import ${PACKAGE_NAME}; print('package version is ', ${PACKAGE_NAME}.__version__)"
@@ -380,7 +388,14 @@ jobs:
           cd $SRC_DIR
           source .venv/Scripts/activate
           whl=$(find dist -name "${{env.PACKAGE_NAME}}-*.whl" | head -n 1)
-          pip install $whl
+          # See the X64 smoke test above: for 3.15 / 3.15t numpy ships only on
+          # download.pytorch.org, as a pre-release.
+          if [[ "${{ startsWith(matrix.python_version, '3.15') }}" == "true" ]]; then
+            pip install --pre "$whl" \
+              --index-url "https://download.pytorch.org/whl/${CHANNEL}/${CU_VERSION}"
+          else
+            pip install "$whl"
+          fi
 
           if [[ ! -f ${SMOKE_TEST_SCRIPT} ]]; then
             echo "${SMOKE_TEST_SCRIPT} not found"