From ebe8fb489cc0c9d153a227732eeda10c3d9fa4e4 Mon Sep 17 00:00:00 2001
From: 0z5a <dezhen.lu@student.uni-tuebingen.de>
Date: Wed, 4 Nov 2026 21:40:47 +0100
Subject: [PATCH] [bugfix] Fix Python-only kernel build default (#2064)

---
 fastvideo-kernel/build.sh                 |  2 +-
 fastvideo-kernel/tests/test_build_arch.py | 30 +++++++++++++++++++++--
 2 files changed, 29 insertions(+), 3 deletions(-)

diff --git a/fastvideo-kernel/build.sh b/fastvideo-kernel/build.sh
index 71745e10c..a0d6a6797 100755
--- a/fastvideo-kernel/build.sh
+++ b/fastvideo-kernel/build.sh
@@ -80,7 +80,7 @@ extension_mode_from_cmake_args() {
         && printf '%s' "${BASH_REMATCH[2]^^}"
 }
 if (( PYTHON_ONLY )); then
-    _explicit_mode="$(extension_mode_from_cmake_args)"
+    _explicit_mode="$(extension_mode_from_cmake_args || true)"
     if [[ -n "${_explicit_mode}" && "${_explicit_mode}" != "OFF" ]]; then
         echo "ERROR: --python-only conflicts with CMAKE_ARGS -DFASTVIDEO_KERNEL_BUILD_EXTENSION=${_explicit_mode}" >&2
         exit 2
diff --git a/fastvideo-kernel/tests/test_build_arch.py b/fastvideo-kernel/tests/test_build_arch.py
index 45a200709..14ca51adc 100644
--- a/fastvideo-kernel/tests/test_build_arch.py
+++ b/fastvideo-kernel/tests/test_build_arch.py
@@ -15,7 +15,11 @@ def _write_executable(path: Path, contents: str) -> None:
 
 
 def _run_build(
-    tmp_path: Path, capability: str, cuda_release: str, cmake_args: str | None = None
+    tmp_path: Path,
+    capability: str,
+    cuda_release: str,
+    cmake_args: str | None = None,
+    extra_args: list[str] | None = None,
 ) -> tuple[subprocess.CompletedProcess[str], Path]:
     kernel_dir = tmp_path / "fastvideo-kernel"
     kernel_dir.mkdir()
@@ -51,7 +55,7 @@ def _run_build(
     if cmake_args is not None:
         env["CMAKE_ARGS"] = cmake_args
     result = subprocess.run(
-        ["bash", "build.sh"],
+        ["bash", "build.sh", *(extra_args or [])],
         cwd=kernel_dir,
         env=env,
         capture_output=True,
@@ -103,3 +107,25 @@ def test_build_script_preserves_explicit_tk_option(tmp_path: Path, option: str)
     assert result.returncode == 0, result.stderr
     assert (result_dir / "cmake_args").read_text().count("-DFASTVIDEO_KERNEL_BUILD_TK=") == 1
     assert f"-DFASTVIDEO_KERNEL_BUILD_TK={option}" in (result_dir / "cmake_args").read_text()
+
+
+@pytest.mark.parametrize("cmake_args", [None, "-DOTHER_OPTION=ON", "-DFASTVIDEO_KERNEL_BUILD_EXTENSION=OFF"])
+@pytest.mark.parametrize("build_args", [["--python-only"], ["--rocm", "--python-only"]])
+def test_python_only_build_defaults_extension_to_off(
+    tmp_path: Path, cmake_args: str | None, build_args: list[str]
+) -> None:
+    result, result_dir = _run_build(tmp_path, "9.0", "13.0", cmake_args, build_args)
+
+    assert result.returncode == 0, result.stderr
+    assert (result_dir / "cmake_args").read_text().count("-DFASTVIDEO_KERNEL_BUILD_EXTENSION=OFF") == 1
+    if cmake_args == "-DOTHER_OPTION=ON":
+        assert cmake_args in (result_dir / "cmake_args").read_text()
+    if "--rocm" in build_args:
+        assert "-DGPU_BACKEND=ROCM" in (result_dir / "cmake_args").read_text()
+
+
+def test_python_only_build_rejects_extension_on(tmp_path: Path) -> None:
+    result, _ = _run_build(tmp_path, "9.0", "13.0", "-DFASTVIDEO_KERNEL_BUILD_EXTENSION=ON", ["--python-only"])
+
+    assert result.returncode != 0
+    assert "--python-only conflicts" in result.stderr