[requests] Add missing attributes and __init__ to JSONDecodeError stub

[sedat4ras]

Fixes #15167

Problem

requests.exceptions.JSONDecodeError inherits from both InvalidJSONError (which inherits from RequestException) and json.JSONDecodeError. When catching it in user code, accessing attributes like exc.doc causes a mypy error:

error: "JSONDecodeError" has no attribute "doc"  [attr-defined]

Root Cause

The runtime requests.JSONDecodeError.__init__ explicitly calls CompatJSONDecodeError.__init__(self, *args) first, which sets the json.JSONDecodeError instance attributes (doc, pos, lineno, colno, msg). However, due to the complex MRO (where RequestException.__init__ appears before json.JSONDecodeError in the chain), type checkers may not correctly resolve these inherited attributes.

Fix

Explicitly re-declare the json.JSONDecodeError attributes on requests.JSONDecodeError and add the correct __init__ signature matching the runtime behavior (msg: str, doc: str, pos: int), consistent with how requests calls it:

raise RequestsJSONDecodeError(e.msg, e.doc, e.pos)

After this fix:

import requests
from requests.exceptions import JSONDecodeError

try:
    requests.get("https://www.google.com").json()
except JSONDecodeError as exc:
    d = exc.doc  # no longer a mypy error
    print("Failed to decode json. Got:", d[:10])

[github-actions]

According to mypy_primer, this change has no effect on the checked open source code. 🤖🎉

[srittau]

Thanks, but this was already fixed in #15167 by deriving requests.JSONDecodeError from json.JSONDecodeError. We just forgot to close the corresponding issue.