[NielBuys]

Implements upstream feature request bcit-ci/CodeIgniter#6335. Full review and decision record: docs/todo/archive/issue-6335-field-data-is-nullable.md.

What it does

Every driver's field_data() now sets is_nullable on each field: 1 if the column accepts NULL, 0 if it is NOT NULL. Drivers that cannot report it return 1, so code reading the property never hits an undefined-property warning, whatever the database.

Scope: real values only where it is safe

The property is additive. For ten drivers, though, a full implementation would change the SQL that field_data() already runs, and a wrong query there would break field_data() for existing callers. The rule applied: report the real value where no query changes or where CI can test the change; otherwise return 1 and leave the query alone.

Table metadata $db->field_data('t')
mysqli, mysql, cubrid, pdo_mysql, pdo_cubrid, sqlite, sqlite3, pdo_sqlite, oci8, pdo_oci	Real value, read from data the query already returns
postgre, pdo_pgsql	Real value; is_nullable added to the SELECT (covered by CI)
mssql, sqlsrv, pdo_dblib, pdo_sqlsrv, ibase, pdo_firebird, pdo_ibm, pdo_informix	1, query unchanged

Result metadata $query->field_data()
mysqli, mysql, cubrid, pdo (where the subdriver reports not_null, i.e. pdo/mysql), sqlsrv	Real value from existing metadata
postgre, oci8, mssql, ibase, sqlite, sqlite3, odbc	1 (no API exists)

The user guide (database/metadata.rst) documents this, including the caveat that result metadata describes the result set: a LEFT JOIN column can be nullable when the base column is not. There is a changelog entry under 3.1.24.

Tests

New tests/codeigniter/database/DB_field_data_test.php runs in the six CI database jobs. Table metadata must report real values on all six; result metadata must be real on mysqli and pdo/mysql and 1 elsewhere.

• Run locally (PHP 8.5.4): sqlite and pdo/sqlite pass. Both new tests fail without the driver changes. The full sqlite suite shows only the existing Calendar_test failure.
• pdo/sqlite needed a temporary local change: its test DSN builds sqlite:/C:/..., which doesn't resolve on Windows, so it was edited for the run and restored.
• Not run locally: mysqli, pdo/mysql, pgsql and pdo/pgsql (no travis user or ci_test database). This PR's CI run is their first test.

Not changed: existing defects recorded in the doc

• pdo_oci_driver::field_data() assigns an unselected COLUMN_DEFAULT, so default is always NULL.
• pdo_ibm_driver::field_data() uses CASE "keyseq" WHEN NULL, which never matches, so every column reports primary_key = 1.
• pdo_informix_driver::field_data() appears to drop columns without a default (unverified).

Housekeeping

mysqli_result.php and pdo_mysql_driver.php had CRLF working copies left over from before .gitattributes. They were re-checked out as LF before editing. The repository content is unaffected.

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