mssql_python: discrete connection fields are silently ignored when connection_string is set

[cofin]

Summary

In the mssql_python adapter, build_connection_config returns early when connection_string is present, so every discrete field in the same connection_config (server, database, uid, pwd, encrypt, extra, ...) is dropped without a warning or error.

# sqlspec/adapters/mssql_python/core.py
connection_string = config.pop("connection_string", None)
if connection_string is not None:
    return str(connection_string), connect_kwargs

Why it matters

A common pattern is to hold one base config and derive per-database configs from it by overriding database:

base = {"connection_string": "Server=host,1433;UID=app;PWD=...;Encrypt=yes;"}
per_db = MssqlPythonConfig(connection_config={**base, "database": "sales"})

per_db connects to the login's default database, not sales. Nothing fails — queries simply run against the wrong database, which is hard to notice when iterating over several databases on one instance.

Reproduction

from sqlspec.adapters.mssql_python.core import build_connection_config

conn_str, _ = build_connection_config(
    {"connection_string": "Server=host;UID=u;PWD=p;", "database": "sales"}
)
assert "sales" in conn_str  # fails: "Server=host;UID=u;PWD=p;"

Expected

Either of these would remove the silent wrong answer:

1. Merge discrete fields with the explicit string, with a documented precedence. The arrow_odbc adapter already does this (its build_connection_config composes the discrete fields and appends connection_string as a suffix, with the precedence described in the docstring), so the two ODBC-style adapters would behave the same way.
2. Raise a ValueError (or ImproperConfigurationError) when connection_string is combined with any connection-string-level field, naming the conflicting keys.

Option 1 seems the friendlier of the two, provided the precedence is stated (an explicit field overriding the same key inside the string is the least surprising for the per-database case above).

Version

sqlspec 0.63.1; still present on main.