Bazel: Protobuf v33 (python) requires @system_python

[Mizux]

What version of protobuf and what language are you using?
Version: v33.0
Language: C++ (pybind11) + Python
Build System: Bazel 8.4.2 (bzlmod)

What operating system (Linux, Windows, ...) and version?

• amd64*Linux
• amd64*MacOS
• amd64*Windows
• aarch64*MacOS

ref:

• https://github.com/google/oss-policies-info/blob/main/foundational-cxx-support-matrix.md
• https://github.com/google/oss-policies-info/blob/main/foundational-python-support-matrix.md

What runtime / compiler are you using (e.g., python version or gcc version)
tested against Python 3.12/3.13

What did you do?
easy to reproduce using this MVE:
https://github.com/Mizux/bazel-pybind11-protobuf (branch dev)

git clone --depth 1 -b dev https://github.com/Mizux/bazel-pybind11-protobuf
cd bazel-pybind11-protobuf
bazel build //bp11/foo/python:all

What did you expect to see
Build pass

What did you see instead?

ERROR: no such package '@@[unknown repo 'system_python' requested from @@protobuf+]//': The repository '@@[unknown repo 'system_python' requested from @@protobuf+]' could not be resolved: No repository visible as '@system_python' from repository '@@protobuf+'
ERROR: /usr/local/google/home/corentinl/.cache/bazel/_bazel_corentinl/0894f505b0c1ca0afddf1fd7c7733baa/external/protobuf+/python/BUILD.bazel:14:14: no such package '@@[unknown repo 'system_python' requested from @@protobuf+]//': The repository '@@[unknown repo 'system_python' requested from @@protobuf+]' could not be resolved: No repository visible as '@system_python' from repository '@@protobuf+' and referenced by '@@protobuf+//python:proto_api'
ERROR: Analysis of target '//bp11/foo/python:pyfoo_copy_so_to_pyd' failed; build aborted: Analysis failed
INFO: Elapsed time: 2.514s, Critical Path: 0.03s
INFO: 1 process: 1 internal.
ERROR: Build did NOT complete successfully

Make sure you include information that can help us debug (full error message, exception listing, stack trace, logs).

Anything else we should know about your project / environment

• perfectly working using Protobuf v32.0 (see main branch).

• perfectly working using Protobuf v33.0 and CMake based build (see dev branch).

• https://github.com/Mizux/bazel-proto (no python) Perfectly work against v33.0 on both build Systems...

Spotted some traces of system_python in rules_python 1.7.0 changelog....... which is not released yet !
ref:

• https://github.com/bazel-contrib/rules_python/releases (1.7 RC only)
• https://github.com/bazelbuild/bazel-central-registry/tree/main/modules/rules_python (no version 1.7*)
• https://rules-python.readthedocs.io/en/latest/changelog.html#v1-7-0

[Mizux]

Still don't understand why protobuf do not rely on "@rules_python//python/cc:current_py_cc_headers" or "@rules_python//python/cc:current_py_cc_libs", to interact nicely with @rules_python registered toolchain(s) setup...

aka I want my MODULE.bazel to be something like this:

bazel_dep(name = "rules_python", version = "1.6.3")
SUPPORTED_PYTHON_VERSIONS = [
    "3.14", # Release 2025/10/07 EOL 2030/10/31
    "3.13", # EOL 2029/10/31
    "3.12", # EOL 2028/10/31
    "3.11", # EOL 2027/31/10
    "3.10", # EOL 2026/10/31
    "3.9", # EOL 2025/10/31
]
DEFAULT_PYTHON = "3.13"
python = use_extension("@rules_python//python/extensions:python.bzl", "python")
[
    python.toolchain(
        ignore_root_user_error = True,  # needed for CI
        is_default = version == DEFAULT_PYTHON,
        python_version = version,
    )
    for version in SUPPORTED_PYTHON_VERSIONS
]
pip = use_extension("@rules_python//python/extensions:pip.bzl", "pip")
[
    pip.parse(
        hub_name = "bp11_pip_deps",
        python_version = version,
        requirements_lock = "//bazel:requirements.txt",
    )
    for version in SUPPORTED_PYTHON_VERSIONS
]
use_repo(pip, pypi = "bp11_pip_deps")

bazel_dep(name = "protobuf", version = "33.0")

and I can control the python version used by cmd line/.bazelrc using --@rules_python//python/config_settings:python_version=3.13 ...

[Mizux]

@rickeylev any help appreciated (or insight on rules_python 1.7 ^v^)...

[Mizux]

after few investigation seems to be pull by @com_google_protobuf//python:proto_api used in @pybind_protobuf (using protobug v29.2).
ref: https://github.com/pybind/pybind11_protobuf/blob/87ec9afa645dbe5d8f1fafe494acd45049ed8211/pybind11_protobuf/BUILD#L50

Manage to reproduce it modifying/hacking the examples/ directory:
note: i'm using protobuf BCR 33.0, need to test using the local_path_override.
note: I've removed the WORKSPACE file to be bzlmod only (one issue at a time...)
EDIT: minimize diff to reproduce it...

git diff -u
diff --git a/examples/BUILD.bazel b/examples/BUILD.bazel
index 87ef598cb..8e2780f5b 100644
--- a/examples/BUILD.bazel
+++ b/examples/BUILD.bazel
@@ -49,6 +49,7 @@ cc_binary(
         ":addressbook_cc_proto",
         "@com_google_protobuf//:protobuf",
         "@com_google_protobuf//src/google/protobuf/util:time_util",
+        "@com_google_protobuf//python:proto_api",
     ],
 )
 
diff --git a/examples/MODULE.bazel b/examples/MODULE.bazel
index ab848dcd8..0b052f2d4 100644
--- a/examples/MODULE.bazel
+++ b/examples/MODULE.bazel
@@ -12,14 +12,35 @@ local_path_override(
     path = "..",
 )
 
-bazel_dep(name = "com_google_protobuf-examples-with-hyphen", version = "0.0.0", dev_dependency = True)
-local_path_override(
-    module_name = "com_google_protobuf-examples-with-hyphen",
-    path = "examples_with_hyphen",
-)
+#bazel_dep(name = "com_google_protobuf-examples-with-hyphen", version = "0.0.0", dev_dependency = True)
+#local_path_override(
+#    module_name = "com_google_protobuf-examples-with-hyphen",
+#    path = "examples_with_hyphen",
+#)
 
-bazel_dep(name = "bazel_skylib", version = "1.7.1")
-bazel_dep(name = "rules_cc", version = "0.0.17")
+bazel_dep(name = "bazel_skylib", version = "1.8.2")
+bazel_dep(name = "rules_cc", version = "0.2.9")
 bazel_dep(name = "rules_java", version = "8.6.1")
 bazel_dep(name = "rules_pkg", version = "1.0.1")
-bazel_dep(name = "rules_python", version = "1.6.0")
+bazel_dep(name = "rules_python", version = "1.6.3")
+
+SUPPORTED_PYTHON_VERSIONS = [
+    "3.14",
+    "3.13",
+    "3.12",
+    "3.11",
+    "3.10",
+    "3.9",
+]
+
+DEFAULT_PYTHON = "3.13"
+python = use_extension("@rules_python//python/extensions:python.bzl", "python")
+
+[
+    python.toolchain(
+        ignore_root_user_error = True,  # needed for CI
+        is_default = version == DEFAULT_PYTHON,
+        python_version = version,
+    )
+    for version in SUPPORTED_PYTHON_VERSIONS
+]

[0]—[~/work/protobuf/examples]—[tags/v4.33.0-objectivec]
[*v*]—[corentinl@corentinl] »bazel build --@rules_python//python/config_settings:python_version=3.13 //...

Definitively need to make a pybind_abseil then pybind_protobuf release

Still one question: is @com_google_protobuf//python:proto_api still needed ? if yes why it depends on system_python ?

[honglooker]

Hmm potential fallout from recent deltas @mkruskal-google ?

[Mizux]

seems to comes from fa9ceb3

I'll take a look at the CL tomorrow to get more info...