format_group_by_params mishandles escaped %% causing IndexError on queries with GROUP BY

[kolatat]

Software versions

• mssql-django: 1.6
• python: 3.12

Problem description and steps to reproduce
When a MSSQL query cursor is executed with parameters, there is an error.
Conditions:

• SQL query with a GROUP BY clause
• an escaped % somewhere in the query (%%)
• valid parameters

Expected behavior and actual behavior
Expected: query is executed, with correct parameters substituted in, and escaped %% treated correctly as % literal.
Actual: error on query execution, saying replacement arguments # mismatched.

Error message/stack trace

IndexError: Replacement index 10 out of range for positional args tuple
...
Traceback (most recent call last):
...
  File "my/views.py", line 3620, in ***
    cursor.execute(sql, [...])

  File ".../lib/python3.12/site-packages/django/db/backends/utils.py", line 122, in execute
    return super().execute(sql, params)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ".../lib/python3.12/site-packages/django/db/backends/utils.py", line 79, in execute
    return self._execute_with_wrappers(
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ".../lib/python3.12/site-packages/django/db/backends/utils.py", line 92, in _execute_with_wrappers
    return executor(sql, params, many, context)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ".../lib/python3.12/site-packages/django/db/backends/utils.py", line 105, in _execute
    return self.cursor.execute(sql, params)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ".../lib/python3.12/site-packages/mssql/base.py", line 672, in execute
    sql, params = self.format_group_by_params(sql, params)
                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ".../lib/python3.12/site-packages/mssql/base.py", line 640, in format_group_by_params
    query = ('DECLARE %s \n' % ','.join(variables)) + (query.format(*args))
                                                       ^^^^^^^^^^^^^^^^^^^
IndexError: Replacement index 10 out of range for positional args tuple

Any other details that can be helpful

in mssql/base.py#L624 (def format_group_by_params), regexp %\w+ is used to substitute %s with {}. This does not account for escaped % (%%), resulting in the mismatched replacements.

[ortkin]

This is also related to #394 and follow up question that’s also linked.