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Use cuda-pathfinder in build-system.requires #1817

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01f33cd
build: use cuda.pathfinder.get_cuda_path_or_home in build hooks
rwgk Mar 24, 2026
0fc4597
chore: update stale pixi package version to 1.5.0
rwgk Mar 24, 2026
3d422de
build: raise actionable error when cuda-pathfinder not found on sys.path
rwgk Mar 25, 2026
73e840e
Merge branch 'main' into pathfinder_in_build-system_requires
rwgk Mar 25, 2026
6892ae0
build: replace inline docstring with reference to issue #1824
rwgk Mar 25, 2026
5a06d6f
Merge branch 'main' into pathfinder_in_build-system_requires
rwgk Mar 31, 2026
b779d0d
build: narrow except to only catch cuda.pathfinder-not-found
rwgk Mar 31, 2026
6facaa5
build: use importlib.metadata to locate cuda-pathfinder instead of sc…
rwgk Mar 31, 2026
f1ef076
build: produce actionable error when cuda namespace is entirely absent
rwgk Mar 31, 2026
3cb0313
build: diagnostic for importlib.metadata locate_file in PEP 517 builds
rwgk Mar 31, 2026
a9995ac
Revert "build: diagnostic for importlib.metadata locate_file in PEP 5…
rwgk Mar 31, 2026
cb5ffbb
build: revert to sys.path scan, importlib.metadata finds wrong dist-info
rwgk Mar 31, 2026
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38 changes: 33 additions & 5 deletions cuda_bindings/build_hooks.py
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Expand Up @@ -33,13 +33,41 @@
_extensions = None


# Please keep in sync with the copy in cuda_core/build_hooks.py.
def _import_get_cuda_path_or_home():
"""Import get_cuda_path_or_home, working around PEP 517 namespace shadowing.

See https://github.com/NVIDIA/cuda-python/issues/1824 for why this helper is needed.
"""
try:
import cuda.pathfinder
except ModuleNotFoundError as exc:
if exc.name not in ("cuda", "cuda.pathfinder"):
raise
try:
import cuda
except ModuleNotFoundError:
cuda = None

for p in sys.path:
sp_cuda = os.path.join(p, "cuda")
if os.path.isdir(os.path.join(sp_cuda, "pathfinder")):
cuda.__path__ = list(cuda.__path__) + [sp_cuda]
break
else:
raise ModuleNotFoundError(
"cuda-pathfinder is not installed in the build environment. "
"Ensure 'cuda-pathfinder>=1.5' is in build-system.requires."
)
import cuda.pathfinder

return cuda.pathfinder.get_cuda_path_or_home


@functools.cache
def _get_cuda_path() -> str:
# Not using cuda.pathfinder.get_cuda_path_or_home() here because this
# build backend runs in an isolated venv where the cuda namespace package
# from backend-path shadows the installed cuda-pathfinder. See #1803 for
# a workaround to apply after cuda-pathfinder >= 1.5 is released.
cuda_path = os.environ.get("CUDA_PATH", os.environ.get("CUDA_HOME"))
get_cuda_path_or_home = _import_get_cuda_path_or_home()
cuda_path = get_cuda_path_or_home()
if not cuda_path:
raise RuntimeError("Environment variable CUDA_PATH or CUDA_HOME is not set")
print("CUDA path:", cuda_path)
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3 changes: 2 additions & 1 deletion cuda_bindings/pyproject.toml
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Expand Up @@ -6,6 +6,7 @@ requires = [
"setuptools_scm[simple]>=8",
"cython>=3.2,<3.3",
"pyclibrary>=0.1.7",
"cuda-pathfinder>=1.5",
]
build-backend = "build_hooks"
backend-path = ["."]
Expand All @@ -31,7 +32,7 @@ classifiers = [
"Environment :: GPU :: NVIDIA CUDA",
]
dynamic = ["version", "readme"]
dependencies = ["cuda-pathfinder >=1.4.2"]
dependencies = ["cuda-pathfinder >=1.5"]

[project.optional-dependencies]
all = [
Expand Down
38 changes: 33 additions & 5 deletions cuda_core/build_hooks.py
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Expand Up @@ -28,13 +28,41 @@
COMPILE_FOR_COVERAGE = bool(int(os.environ.get("CUDA_PYTHON_COVERAGE", "0")))


# Please keep in sync with the copy in cuda_bindings/build_hooks.py.
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@rparolin rparolin Mar 25, 2026

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We should avoid duplicating implementations. Could we not hoist this into a separate file and import from both?

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@rwgk rwgk Mar 25, 2026

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We should avoid duplicating implementations.

Agreed

Could we not hoist this into a separate file and import from both?

No 😭

In the words of Cursor Opus 4.6 1M Thinking:

There's no reasonable way to share code between the two build_hooks.py files:

  • Each is a PEP 517 build backend loaded via backend-path=["."] from its own package directory (cuda_bindings/ or cuda_core/). They can't import from the monorepo root or from each other.
  • The function exists because cuda.pathfinder can't be imported normally in this context — so it can't live inside cuda-pathfinder either.
  • A shared helper package in build-system.requires would be massive overkill for ~15 lines of stable code.

The only alternatives are worse: a new PyPI package just for this, importlib file-path hacks, or copying a shared file into both directories at CI time.

The "please keep in sync" comments are the pragmatic solution here.

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@rwgk rwgk Mar 25, 2026

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We have other existing cases of "please keep in sync" that are impractical to avoid.

It just crossed my mind: a pre-commit check to enforce that they stay in sync is probably pretty easy to implement.

def _import_get_cuda_path_or_home():
"""Import get_cuda_path_or_home, working around PEP 517 namespace shadowing.

See https://github.com/NVIDIA/cuda-python/issues/1824 for why this helper is needed.
"""
try:
import cuda.pathfinder
except ModuleNotFoundError as exc:
if exc.name not in ("cuda", "cuda.pathfinder"):
raise
try:
import cuda
except ModuleNotFoundError:
cuda = None

for p in sys.path:
sp_cuda = os.path.join(p, "cuda")
if os.path.isdir(os.path.join(sp_cuda, "pathfinder")):
cuda.__path__ = list(cuda.__path__) + [sp_cuda]
break
else:
raise ModuleNotFoundError(
"cuda-pathfinder is not installed in the build environment. "
"Ensure 'cuda-pathfinder>=1.5' is in build-system.requires."
)
import cuda.pathfinder
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@rparolin rparolin Mar 25, 2026

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Should we include some message explaining that we iterated through sys.path looking for pathfinder and couldn't find it? That seems to be important information that would be missing from just throwing we couldn't import pathfinder module.

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@rparolin rparolin Mar 25, 2026

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          for p in sys.path:
              sp_cuda = os.path.join(p, "cuda")                                                                                
              if os.path.isdir(os.path.join(sp_cuda, "pathfinder")):
                  cuda.__path__ = list(cuda.__path__) + [sp_cuda]                                                              
                  break                 
          else:                                                                                                                
              raise ModuleNotFoundError(
                  "cuda-pathfinder is not installed in the build environment. "                                                
                  "Ensure 'cuda-pathfinder>=1.5' is in build-system.requires."                                                 
              )
          import cuda.pathfinder ```

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@rwgk rwgk Mar 25, 2026

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Done: commit 3d422de


return cuda.pathfinder.get_cuda_path_or_home


@functools.cache
def _get_cuda_path() -> str:
# Not using cuda.pathfinder.get_cuda_path_or_home() here because this
# build backend runs in an isolated venv where the cuda namespace package
# from backend-path shadows the installed cuda-pathfinder. See #1803 for
# a workaround to apply after cuda-pathfinder >= 1.5 is released.
cuda_path = os.environ.get("CUDA_PATH", os.environ.get("CUDA_HOME"))
get_cuda_path_or_home = _import_get_cuda_path_or_home()
cuda_path = get_cuda_path_or_home()
if not cuda_path:
raise RuntimeError("Environment variable CUDA_PATH or CUDA_HOME is not set")
print("CUDA path:", cuda_path)
Expand Down
3 changes: 2 additions & 1 deletion cuda_core/pyproject.toml
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Expand Up @@ -7,6 +7,7 @@ requires = [
"setuptools>=80",
"setuptools-scm[simple]>=8",
"Cython>=3.2,<3.3",
"cuda-pathfinder>=1.5"
]
build-backend = "build_hooks"
backend-path = ["."]
Expand Down Expand Up @@ -47,7 +48,7 @@ classifiers = [
"Environment :: GPU :: NVIDIA CUDA :: 13",
]
dependencies = [
"cuda-pathfinder >=1.4.2",
"cuda-pathfinder >=1.5",
"numpy",
]

Expand Down
7 changes: 6 additions & 1 deletion cuda_core/tests/test_build_hooks.py
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@@ -1,4 +1,4 @@
# SPDX-FileCopyrightText: Copyright (c) 2024-2025 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
# SPDX-FileCopyrightText: Copyright (c) 2024-2026 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
# SPDX-License-Identifier: Apache-2.0

"""Tests for build_hooks.py build infrastructure.
Expand All @@ -24,6 +24,8 @@

import pytest

from cuda.pathfinder import get_cuda_path_or_home

# build_hooks.py imports Cython and setuptools at the top level, so skip if not available
pytest.importorskip("Cython")
pytest.importorskip("setuptools")
Expand Down Expand Up @@ -68,6 +70,7 @@ def _check_version_detection(

build_hooks._get_cuda_path.cache_clear()
build_hooks._determine_cuda_major_version.cache_clear()
get_cuda_path_or_home.cache_clear()

mock_env = {
k: v
Expand All @@ -92,6 +95,7 @@ def test_env_var_override(self, version):
"""CUDA_CORE_BUILD_MAJOR env var override works with various versions."""
build_hooks._get_cuda_path.cache_clear()
build_hooks._determine_cuda_major_version.cache_clear()
get_cuda_path_or_home.cache_clear()
with mock.patch.dict(os.environ, {"CUDA_CORE_BUILD_MAJOR": version}, clear=False):
result = build_hooks._determine_cuda_major_version()
assert result == version
Expand Down Expand Up @@ -125,6 +129,7 @@ def test_missing_cuda_path_raises_error(self):
"""RuntimeError is raised when CUDA_PATH/CUDA_HOME not set and no env var override."""
build_hooks._get_cuda_path.cache_clear()
build_hooks._determine_cuda_major_version.cache_clear()
get_cuda_path_or_home.cache_clear()
with (
mock.patch.dict(os.environ, {}, clear=True),
pytest.raises(RuntimeError, match="CUDA_PATH or CUDA_HOME"),
Expand Down
2 changes: 1 addition & 1 deletion cuda_pathfinder/pixi.toml
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Expand Up @@ -36,7 +36,7 @@ cu12 = { features = ["cu12", "test"], solve-group = "cu12" }
# TODO: check if these can be extracted from pyproject.toml
[package]
name = "cuda-pathfinder"
version = "1.3.4a0"
version = "1.5.0"

[package.build]
backend = { name = "pixi-build-python", version = "*" }
Expand Down
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