Build cuda.core RDC test fixtures without Bash (#2335)

* Run nvcc fixture build without Bash

* Document narrow nvcc skip detection

* Document nvcc test environment requirements

Author: rwgk

.github/workflows/build-wheel.yml

@@ -463,7 +463,9 @@ jobs:
           cuda-path: "./cuda_toolkit_prev"
 
       - name: Build cuda.core test binaries
-        run: bash ${{ env.CUDA_CORE_TEST_BINARIES_DIR }}/build_test_binaries.sh
+        run: |
+          nvcc --version
+          python "${{ env.CUDA_CORE_TEST_BINARIES_DIR }}/build_test_binaries.py"
 
       - name: Upload cuda.core test binaries
         uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a  # v7.0.1

cuda_core/tests/test_binaries/build_test_binaries.py

@@ -0,0 +1,56 @@
+# SPDX-FileCopyrightText: Copyright (c) 2026 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
+# SPDX-License-Identifier: Apache-2.0
+"""Build the relocatable-device-code fixtures used by cuda.core tests."""
+
+from __future__ import annotations
+
+import os
+import subprocess
+import tempfile
+from pathlib import Path
+
+
+def _run(command: list[str]) -> None:
+    print(f"+ {subprocess.list2cmdline(command)}")
+    result = subprocess.run(command)  # noqa: S603
+    if result.returncode != 0:
+        raise SystemExit(result.returncode)
+
+
+def main() -> None:
+    script_dir = Path(__file__).resolve().parent
+    source_path = script_dir / "saxpy.cu"
+    final_object_path = script_dir / "saxpy.o"
+    final_library_path = script_dir / ("saxpy.lib" if os.name == "nt" else "saxpy.a")
+
+    nvcc_extra_flags = ["-std=c++17"]
+    if os.name == "nt":
+        nvcc_extra_flags.extend(["-Xcompiler", "/Zc:preprocessor"])
+
+    with tempfile.TemporaryDirectory(prefix="build_test_binaries-", dir=script_dir) as temp_dir:
+        temp_dir_path = Path(temp_dir)
+        object_path = temp_dir_path / final_object_path.name
+        library_path = temp_dir_path / final_library_path.name
+
+        _run(
+            [
+                "nvcc",
+                "-dc",
+                *nvcc_extra_flags,
+                "-arch=all-major",
+                "-o",
+                str(object_path),
+                str(source_path),
+            ]
+        )
+        _run(["nvcc", "-lib", "-o", str(library_path), str(object_path)])
+
+        object_path.replace(final_object_path)
+        library_path.replace(final_library_path)
+
+    for path in (final_object_path, final_library_path):
+        print(f"{path}: {path.stat().st_size} bytes")
+
+
+if __name__ == "__main__":
+    main()

cuda_core/tests/test_binaries/build_test_binaries.sh

@@ -5,6 +5,7 @@
 import os
 import pickle
 import subprocess
+import sys
 import warnings
 from pathlib import Path
 
@@ -16,7 +17,6 @@
 from cuda.core._program import _can_load_generated_ptx
 from cuda.core._utils.cuda_utils import CUDAError, driver, handle_return
 from cuda.core._utils.version import binding_version, driver_version
-from cuda.pathfinder import find_nvidia_binary_utility
 
 try:
     import numba
@@ -193,22 +193,78 @@ def _read_saxpy_rdc(kind: str) -> bytes:
         raise ValueError(f"unknown saxpy RDC kind: {kind!r}")
 
     if not rdc_path.is_file():
-        nvcc_path = find_nvidia_binary_utility("nvcc")
-        if nvcc_path is None:
-            pytest.skip(
-                f"{rdc_path.name} not found at {rdc_path} and nvcc is unavailable. "
-                "In CI this is downloaded from the build stage."
-            )
-        env = os.environ.copy()
-        env["NVCC"] = nvcc_path
-        subprocess.run(  # noqa: S603
-            ["bash", str(binaries_dir / "build_test_binaries.sh")],  # noqa: S607
-            check=True,
-            env=env,
-        )
+        _build_saxpy_rdc(binaries_dir)
     return rdc_path.read_bytes()
 
 
+def _subprocess_output(result: subprocess.CompletedProcess[str]) -> str:
+    sections = []
+    if result.stdout:
+        sections.append(f"stdout:\n{result.stdout.rstrip()}")
+    if result.stderr:
+        sections.append(f"stderr:\n{result.stderr.rstrip()}")
+    return "\n".join(sections) or "<no output>"
+
+
+def _host_compiler_is_unavailable(output: str) -> bool:
+    normalized = output.lower()
+    # Keep these patterns narrow. Unknown nvcc failures should fail the test and
+    # expose their diagnostics, not be silently reclassified as environment skips.
+    windows_compiler_missing = (
+        "cannot find compiler" in normalized and "cl.exe" in normalized and "in path" in normalized
+    )
+    linux_compiler_missing = (
+        "no such file or directory" in normalized and "failed to preprocess host compiler properties" in normalized
+    )
+    return windows_compiler_missing or linux_compiler_missing
+
+
+def _build_saxpy_rdc(binaries_dir: Path) -> None:
+    """Use nvcc from PATH with the host compiler environment configured by the caller."""
+    try:
+        version_result = subprocess.run(
+            ["nvcc", "--version"],  # noqa: S607 - PATH lookup is the behavior under test.
+            capture_output=True,
+            text=True,
+            errors="replace",
+        )
+    except FileNotFoundError:
+        pytest.skip("RDC test fixtures are absent and nvcc is not available on PATH")
+
+    if version_result.returncode != 0:
+        pytest.fail(
+            f"nvcc --version failed with exit code {version_result.returncode}\n{_subprocess_output(version_result)}",
+            pytrace=False,
+        )
+
+    print(version_result.stdout, end="")
+    if version_result.stderr:
+        print(version_result.stderr, end="", file=sys.stderr)
+
+    builder_path = binaries_dir / "build_test_binaries.py"
+    build_result = subprocess.run(  # noqa: S603
+        [sys.executable, str(builder_path)],
+        capture_output=True,
+        text=True,
+        errors="replace",
+    )
+    if build_result.returncode == 0:
+        print(build_result.stdout, end="")
+        if build_result.stderr:
+            print(build_result.stderr, end="", file=sys.stderr)
+        return
+
+    output = _subprocess_output(build_result)
+    if _host_compiler_is_unavailable(output):
+        print(output, file=sys.stderr)
+        pytest.skip("nvcc is available, but its host compiler is not configured")
+
+    pytest.fail(
+        f"RDC test fixture build failed with exit code {build_result.returncode}\n{output}",
+        pytrace=False,
+    )
+
+
 def test_get_kernel(init_cuda):
     kernel = """extern "C" __global__ void ABC() { }"""