Cannot deploy multiple flows that use the same proto-plus Message class with Prefect 3

[jmesterh]

Bug summary

We're trying to update to Prefect 3 (from 2), when running prefect deploy --all, if more than one deployment imports the same class with a base class of "proto.Message", the second deployment fails with TypeError: Couldn't build proto file into descriptor pool: duplicate symbol '_default_package.<Class>'.

Calling prefect deploy twice (once for each deployment) is a possible work-around, but this all works fine in Prefect 2.x, using the same version of proto-plus.

protobuf-1.py:

from prefect import flow
from .message import FooMessage

@flow
async def flow_1():
    pass

protobuf-2.py:

from prefect import flow
from .message import FooMessage

@flow
async def flow_2():
    pass

message.py:

import proto

class FooMessage(proto.Message):
    foo = proto.Field(proto.STRING, number=1)

deployment.yaml:

deployments:
  - name: flow 1
    entrypoint: protobuf-1.py:flow_1
    work_pool:
      name: process-pool
  - name: flow 2
    entrypoint: protobuf-2.py:flow_2
    work_pool:
      name: process-pool

$ prefect --no-prompt deploy  --all
Deploying flows with selected deployment configurations...
(flow-1 deploys successfully) 
│ Deploying flow 2                                                                                                                                                 │
Traceback (most recent call last):
  File "<frozen importlib._bootstrap_external>", line 940, in exec_module
  File "<frozen importlib._bootstrap>", line 241, in _call_with_frames_removed
  File "protobuf-2.py", line 4, in <module>
    from .message import FooMessage
  File "message.py", line 4, in <module>
    class FooMessage(proto.Message):
  File "message.py", line 279, in __new__
    file_info.generate_file_pb(new_class=cls, fallback_salt=full_name)
  File ".venv/lib/python3.11/site-packages/proto/_file_info.py", line 104, in generate_file_pb
    pool.Add(self.descriptor)
TypeError: Couldn't build proto file into descriptor pool: duplicate symbol '_default_package.FooMessage'

Version info

Version:             3.2.2
API version:         0.8.4
Python version:      3.11.11
Git commit:          d982c69a
Built:               Thu, Feb 13, 2025 10:53 AM
OS/Arch:             linux/aarch64
Profile:             ephemeral
Server type:         server
Pydantic version:    2.9.2
Integrations:
  prefect-sqlalchemy: 0.5.2
  prefect-dask:      0.3.2
  prefect-docker:    0.6.2
  prefect-dbt:       0.6.6
  prefect-gcp:       0.6.2
  prefect-slack:     0.3.1
  prefect-shell:     0.3.1

protobuf==5.29.3
proto-plus==1.26.0

Additional context

No response

[jmesterh]

This seems related to #16458, where previously the module_name was always "__prefect_loader__" but is now different (for thread safety) f"__prefect_loader_{id(path)}__".

Proto-plus generates file descriptors based on the module name, this change places the same Message descriptor under two different names which is not allowed.