[BUG] OpenAPI Generator’s -g python-flask generator to scaffold a Connexion/Flask server

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

OpenAPI Generator’s -g python-flask generator to scaffold a Connexion/Flask server.
A filename with single underscores (e.g. foo_bar_controller.py)

An operationId (and thus Connexion import path) with doubled underscores (e.g. foo__bar_controller) or stray symbols
This leads Connexion to throw import errors, because the module it expects doesn’t exist.

Controller file: foo_bar_controller.py
Connexion looks for module: foo__bar_controller.py (double underscore)
Server fails to start due to missing module

openapi-generator version

openapi-generator-cli 7.13.0
commit : 4b805ff
built : -999999999-01-01T00:00:00+18:00
source : https://github.com/openapitools/openapi-generator
docs : https://openapi-generator.tech/

PRETTY_NAME="Debian GNU/Linux 13 (trixie)"
NAME="Debian GNU/Linux"
VERSION_ID="13"
VERSION="13 (trixie)"
VERSION_CODENAME=trixie
DEBIAN_VERSION_FULL=13.0
ID=debian
HOME_URL="https://www.debian.org/"
SUPPORT_URL="https://www.debian.org/support"
BUG_REPORT_URL="https://bugs.debian.org/"

OpenAPI declaration file content or url

If you post the code inline, please wrap it with

openapi: 3.0.3
info:
  title: Test API
  version: '1.0'
paths:
  /foo-bar:
    get:
      summary: Get FooBar
      responses:
        '200':
          description: OK

Generation Details

Python 3.12.2

Steps to reproduce

openapi-generator-cli generate
-i openapi.yaml
-g python-flask
-o stub

Suggest a fix

regex brute force

# openapi_server/__main__.py
import re
import connexion
from connexion.resolver import RestyResolver

class CleanResolver(RestyResolver):
    def resolve(self, operation):
        # 1) Take the raw operationId (either from your spec or inferred by Resty)
        raw = super().resolve_operation_id(operation)

        # 2) Replace any non-alphanumeric/underscore/dot with underscore (drops '&', '-', etc.)
        cleaned = re.sub(r'[^A-Za-z0-9_.]', '_', raw)

        # 3) Collapse any runs of multiple underscores into a single one
        cleaned = re.sub(r'__+', '_', cleaned)

        # 4) Let RestyResolver turn that cleaned string into a function
        func = self.resolve_function_from_operation_id(cleaned)
        return connexion.resolver.Resolution(func, cleaned)

app = connexion.FlaskApp(__name__, specification_dir="./stub")
app.add_api(
    "openapi.yaml",
    resolver=CleanResolver("openapi_server.controllers"),
)

if __name__ == "__main__":
    app.run(port=8080, debug=True)

Reproduce the issue with the supplied OpenAPI declaration using the openapi-generator-cli python-flask command, then inspect the generated openapi_server scaffold and its Connexion import paths. Confirm how single and doubled underscores or stray symbols are transformed; done means the generated server starts without missing-module import errors.