Runfiles `Rlocation()` call without `source_repo` param fails in custom python package

まず、リンク先の行にある python/runfiles/runfiles.py、特に Rlocation() と CurrentRepository() から確認し、次に PYTHONPATH を runfiles ディレクトリの外部に設定して、提供されている最小再現を実行します。カスタムパッケージが source_repo なしで Rlocation() を呼び出せ、再現で示された ValueError が発生しなくなれば完了です。

🐞 bug report

Affected Rule

python.runfiles Rlocation()

Is this a regression?

No

Description

When we call Rlocation() inside of a custom python package without passing in the source_repo= parameter and import our package for use elsewhere, if sys.path includes a path to our package's code that is outside the runfiles directory, then the Rlocation() call will fail.

Specifically, this is caused by the code here, which attempts to look up runfiles using the repository mapping of the caller of the Rlocation() method. If sys.path has found and run the copy of our python package that resides outside of the runfiles directory, then the Rlocation() call is legitimately coming from outside the runfiles directory, causing the underlying call to self.CurrentRepository() to fail.

A custom package which calls Rlocation() shouldn't be required to provide the source_repo= parameter or else run the risk of error due to being found outside of the runfiles directory due to the configuration of sys.path.

🔬 Minimal Reproduction

MODULE.bazel

module(name = "reproducer")

bazel_dep(
    name = "rules_python",
    version = "1.9.0"
)

python = use_extension("@rules_python//python/extensions:python.bzl", "python")
python.toolchain(
    python_version = "3.14",
)

BUILD.bazel

load("@rules_python//python:py_binary.bzl", "py_binary")
load("@rules_python//python:py_library.bzl", "py_library")

py_binary(
    name = "binary",
    srcs = ["binary.py"],
    deps = [":library"],
    visibility = ["//visibility:public"],
)

py_library(
    name = "library",
    srcs = ["library/__init__.py"],
    deps = ["@rules_python//python/runfiles"],
    visibility = ["//visibility:public"],
)

binary.py

from library import rlocation_wrapper

if __name__ == "__main__":
    rlocation_wrapper()

library/__init__.py

from python.runfiles import Runfiles


def rlocation_wrapper() -> None:
    runfiles_obj = Runfiles.Create()
    print(runfiles_obj.Rlocation("library/__init__"))

In order to have sys.path find the package outside the runfiles directory, we can set the PYTHONPATH environment variable to the outer folder containing the package.
To reproduce the failure, run:

export PYTHONPATH=/home/<username>/<reproduction_folder>
bazelisk run //:binary

🔥 Exception or Error

ValueError: /home/<username>/<reproduction_folder>/library/__init__.py does not lie under the runfiles root /home/<username>/.cache/bazel/_bazel_<username>/0123456789abcdef0123456789abcdef/execroot/_main/bazel-out/k8-fastbuild/bin/binary.runfiles

Full traceback:

Traceback (most recent call last):
  File "/home/<username>/.cache/bazel/_bazel_<username>/0123456789abcdef0123456789abcdef/execroot/_main/bazel-out/k8-fastbuild/bin/binary.runfiles/_main/_binary_stage2_bootstrap.py", line 537, in <module>
    main()
    ~~~~^^
  File "/home/<username>/.cache/bazel/_bazel_<username>/0123456789abcdef0123456789abcdef/execroot/_main/bazel-out/k8-fastbuild/bin/binary.runfiles/_main/_binary_stage2_bootstrap.py", line 531, in main
    _run_py_path(main_filename, args=sys.argv[1:])
    ~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/<username>/.cache/bazel/_bazel_<username>/0123456789abcdef0123456789abcdef/execroot/_main/bazel-out/k8-fastbuild/bin/binary.runfiles/_main/_binary_stage2_bootstrap.py", line 319, in _run_py_path
    runpy.run_path(main_filename, run_name="__main__")
    ~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "<frozen runpy>", line 287, in run_path
  File "<frozen runpy>", line 98, in _run_module_code
  File "<frozen runpy>", line 88, in _run_code
  File "/home/<username>/.cache/bazel/_bazel_<username>/0123456789abcdef0123456789abcdef/execroot/_main/bazel-out/k8-fastbuild/bin/binary.runfiles/_main/binary.py", line 4, in <module>
    rlocation_wrapper()
    ~~~~~~~~~~~~~~~~~^^
  File "/home/<username>/<reproduction_folder>/library/__init__.py", line 6, in rlocation_wrapper
    print(runfiles_obj.Rlocation("library/__init__"))
          ~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^
  File "/home/<username>/.cache/bazel/_bazel_<username>/0123456789abcdef0123456789abcdef/execroot/_main/bazel-out/k8-fastbuild/bin/binary.runfiles/rules_python+/python/runfiles/runfiles.py", line 306, in Rlocation
    source_repo = self.CurrentRepository(frame=2)
  File "/home/<username>/.cache/bazel/_bazel_<username>/0123456789abcdef0123456789abcdef/execroot/_main/bazel-out/k8-fastbuild/bin/binary.runfiles/rules_python+/python/runfiles/runfiles.py", line 404, in CurrentRepository
    raise ValueError(
    ...<3 lines>...
    )
ValueError: /home/<username>/<reproduction_folder>/library/__init__.py does not lie under the runfiles root /home/<username>/.cache/bazel/_bazel_<username>/0123456789abcdef0123456789abcdef/execroot/_main/bazel-out/k8-fastbuild/bin/binary.runfiles

🌍 Your Environment

Operating System:

Ubuntu 24.04.4 LTS

Output of bazelisk version:

bazel 9.1.0

Rules_python version:

1.9.0