google-cloud-compute fails to import on Python 3.14 — protobuf<5 pins incompatible protobuf 4.x (TypeError: Metaclasses with custom tp_new are not supported)

### Determine this is the right repository - [x] I determined this is the correct repository in which to report this bug. ### Summary of the issue **Context** I upgraded our project to Python 3.14 (CPython 3.14.7, via mise/uv). google-cloud-compute is a direct dependency (currently ==1.15.0). Its metadata declares `protobuf>=3.19.5,<5.0.0dev`, so the resolver installs the newest allowed protobuf on the 4.x line. **Expected Behavior:** `import google.cloud.compute` works on Python 3.14, the same way it works on 3.11–3.13. **Actual Behavior:** Importing the package (or any package that pulls in protobuf, e.g. temporalio) immediately raises `TypeError: Metaclasses with custom tp_new are not supported.` on Python 3.14. protobuf 4.x ships a C extension whose metaclass uses a custom `tp_new`, which CPython 3.14 now rejects. The `protobuf<5` upper bound blocks the only line (protobuf 6.x) whose C extension is fixed for 3.14. ### API client name and version google-cloud-compute==1.15.0 ### Reproduction steps: code file: main.py ```python import google.cloud.compute # raises TypeError on Python 3.14 print("ok") ### Reproduction steps: supporting files No extra data files are required. The only relevant constraint is the version pin resolved from the dependency: file: requirements.txt (minimal) google-cloud-compute==1.15.0 ### Reproduction steps: actual results $ python3 -c "import google.cloud.compute" Traceback (most recent call last): File "<string>", line 1, in <module> File ".../site-packages/google/cloud/compute/__init__.py", line 18, in <module> ... File ".../site-packages/google/protobuf/internal/api_implementation.py", line 51, in <module> if _CanImport('google._upb._message'): File ".../site-packages/google/protobuf/internal/api_implementation.py", line 41, in _CanImport mod = importlib.import_module(mod_name) File ".../lib/python3.14/importlib/__init__.py", line 88, in import_module return _bootstrap._gcd_import(name, level) TypeError: Metaclasses with custom tp_new are not supported. Setting PROTOCOL_BUFFERS_PYTHON_IMPLEMENTATION=python does NOT help: protobuf probes google._upb._message first and the probe itself raises TypeError (not ImportError), so the pure-Python fallback never engages. ### Reproduction steps: expected results $ python3 -c "import google.cloud.compute" ok ### OS & version + platform macOS 27 (Golden Gate), Apple Silicon (arm64) ### Python environment Python 3.14.7 ### Python dependencies pip list | grep -iE "protobuf|google-cloud-compute|google-api-core|proto-plus" google-api-core 2.27.0 google-cloud-compute 1.15.0 proto-plus 1.26.1 protobuf 4.25.9 # forced by google-cloud-compute <5.0.0dev ### Additional context Root cause google-cloud-compute pins `protobuf>=3.19.5,<5.0.0dev`. On Python 3.14: - protobuf 4.25.9 (highest allowed) -> C extension fails with `TypeError: Metaclasses with custom tp_new are not supported.` (CPython 3.14 forbids custom-tp_new metaclasses). - protobuf 6.x (C extension fixed for 3.14) -> blocked by the <5 upper bound. This is a hard deadlock for anyone running google-cloud-compute on Python 3.14. Evidence that 6.x works at runtime We forced protobuf 6.33.6 (uv `override-dependencies = ["protobuf>=6.31.0,<7"]`) and verified on Python 3.14.7: - import google.cloud.compute -> OK - import temporalio (also protobuf-dependent) -> OK - protobuf message serialization round-trips -> OK - temporalio generated *_pb2 round-trips -> OK So the <5 upper bound is overly conservative; the client runs fine on protobuf 6.x. Suggested fix Loosen the protobuf upper bound in google-cloud-compute, e.g. to <8.0.0 (consistent with the other google-cloud-* clients) or at least <7.0.0, and add a Python 3.14 CI job so this regression is caught earlier. Workaround (for affected users) - With uv: override-dependencies = ["protobuf>=6.31.0,<7"] in [tool.uv]. - With pip: pip install --no-deps "google-cloud-compute==1.15.0" "protobuf>=6.31.0" then resolve the rest normally. Related: temporalio already allows protobuf>=3.20,<8.0.0, confirming 6.x is the intended target line.