Schema-qualified table names break under bracket escaping in MSSQL migrations

[pabl-o-ce]

Bug

File: sqlx-mssql/src/migrate.rs

The escape_table_name helper wraps the entire table_name in brackets:

fn escape_table_name(table_name: &str) -> String {
    format!("[{}]", table_name.replace(']', "]]"))
}

When table_name is schema-qualified (e.g., dbo._sqlx_migrations), the result is [dbo._sqlx_migrations] — MSSQL treats this as a single identifier, not schema.table. The correct output should be [dbo].[_sqlx_migrations].

This is a pre-existing issue — the old unescaped code happened to work because the dot was unquoted. The bracket-wrapping fix for #4 preserves the same limitation.

Note: the other drivers (Postgres, MySQL, SQLite) have the same gap — they all interpolate table_name raw without schema-aware splitting.

Context

• dangerous_set_table_name() docs explicitly state the name "may be schema-qualified"
• Relates to fix in SQL injection: unescaped table_name in migration SQL #4

Suggested Fix

Split table_name on . and escape each segment individually:

fn escape_table_name(table_name: &str) -> String {
    table_name
        .split('.')
        .map(|part| format!("[{}]", part.replace(']', "]]")))
        .collect::<Vec<_>>()
        .join(".")
}

This should also be considered for the other drivers using their respective quoting styles.