[18.0][IMP] report_py3o: improve error observability in LO conversion chain

[rrebollo]

Problem

When LibreOffice fails to convert a rendered ODT to the target format, FileNotFoundError propagates unhandled, the controller catches it without logging, and debugging is impossible.

Actual production traceback (anonymized):

  File ".../reporting-engine/report_py3o/controllers/main.py", line 82, in report_download
    response = self.report_routes(
  File ".../odoo/http.py", line 754, in route_wrapper
    result = endpoint(self, *args, **params_ok)
  File ".../reporting-engine/report_xml/controllers/report.py", line 24, in report_routes
    return super().report_routes(
  File ".../odoo/http.py", line 754, in route_wrapper
    result = endpoint(self, *args, **params_ok)
  File ".../reporting-engine/report_xlsx_helper/controllers/main.py", line 51, in report_routes
    return super().report_routes(reportname, docids, converter, **data)
  File ".../odoo/http.py", line 754, in route_wrapper
    result = endpoint(self, *args, **params_ok)
  File ".../reporting-engine/report_xlsx/controllers/main.py", line 51, in report_routes
    return super().report_routes(reportname, docids, converter, **data)
  File ".../odoo/http.py", line 754, in route_wrapper
    result = endpoint(self, *args, **params_ok)
  File ".../reporting-engine/report_py3o/controllers/main.py", line 47, in report_routes
    res, filetype = ir_action._render(reportname, docids, data)
  File ".../odoo/addons/base/models/ir_actions_report.py", line 1135, in _render
    return render_func(report_ref, res_ids, data=data)
  File ".../reporting-engine/report_py3o/models/ir_actions_report.py", line 171, in _render_py3o
    .create_report(res_ids, data)
  File ".../reporting-engine/report_py3o/models/py3o_report.py", line 394, in create_report
    with open(result_path, "r+b") as fd:

FileNotFoundError: [Errno 2] No such file or directory:
    '/tmp/p3o.report.tmp.xxxxxxxx.pdf'

The FileNotFoundError is not the root cause — it is the last symptom of a silent failure chain:

1. LibreOffice runs --headless --convert-to → exit code 0 → but silently produces no output file (e.g. because the rendered ODT contains HTML content LO cannot handle)
2. _convert_single_report has zero error handling — subprocess.check_output succeeds, code computes the expected output path, never verifies the file exists
3. create_report tries open(result_path, "r+b") → FileNotFoundError propagates
4. Controller's except Exception does not log — the entire traceback is silently swallowed, returned as JSON to the browser, and lost on page refresh

Fix

Two minimal changes following OCA patterns already used by sibling addons (report_csv, report_xlsx, report_xml):

py3o_report.py — Model-level error handling:

• Capture LO stderr: subprocess.check_output(..., stderr=subprocess.STDOUT)
• try/except FileNotFoundError → UserError
• try/except CalledProcessError → logger.error(details) + UserError
• Post-conversion: os.path.exists(result_path) → logger.error(stderr) + UserError if missing
• _convert_single_report_cmd: RuntimeError → UserError

controllers/main.py — Controller-level logging (one line):

• logger.exception("Error while generating py3o report: %s", reportname) before serialize_exception
• Matches report_csv, report_xlsx, report_xml controllers exactly

Testing

Two new tests added:

Test	Pattern	Verifies
test_convert_single_report_called_process_error	TransactionCase + mock.patch("subprocess.check_output")	_convert_single_report raises UserError on LO failure
TestReportPy3oController.test_report_download_error_logging	HttpCase + mock.patch.object(ReportController, "report_routes") + assertLogs	Controller logs before serializing error JSON

@BinhexTeam T18747

[fsmw]

Thanks @rrebollo for the reciprocal review opportunity — happy to return the favor on #1165.

Solid PR. Confirmed the controller pattern matches report_csv (line 107) and report_xlsx (line 101) exactly: logger.exception before serialize_exception. Good catch on the missing os.path.exists check — that's the real root cause of the silent LO exit-0-with-no-output chain (we hit a similar issue once with HTML content in templates).

The RuntimeError → UserError change is also correct and the existing test_py3o_report_availability already covers that path at line 264.

CI all green (pre-commit, Odoo, OCB, codecov, runboat), tests are appropriately focused (TransactionCase for the model path, HttpCase + assertLogs for the controller), and the localized error messages + stderr context in logger.error are exactly what admins need for postmortem.

Approved ✅