Fix: Preserve description field during user sync to prevent being reset to '1'

[birdy1976]

Description

This fix resolves an issue where the user description field was being reset to '1' on every user sync when no explicit field mapping was configured.

Root Cause

Commit 7e07704 ("Further performance improvements") removed code that explicitly preserved the description field with the assumption that get_complete_user_data() would properly load all user fields including custom profile fields.

However, get_complete_user_data() does not reliably load custom profile fields. When the description field was missing from the user object passed to apply_configured_fieldmap(), it would get defaulted to empty/'1' even when no mapping was configured for it.

Solution

This restores the two lines of code that explicitly fetch and preserve the current description field value before calling apply_configured_fieldmap():

$existingusercopy = core_user::get_user_by_username($existinguser->username);
$fullexistinguser->description = $existingusercopy->description;

This ensures the description field is always available, preventing it from being unexpectedly overwritten.

Changes

• File: classes/feature/usersync/main.php
• Lines: 1773-1774 (2 lines added)
• Impact: Minimal (restores previously-working code)
• Performance: Negligible (one additional DB query per synced user)
• Risk: Very low (revert of a broken optimization)

Testing

✓ Syntax validation passed
✓ Code reviewed against git history
✓ Follows previous implementation pattern

Affected Versions

This fix applies to:

• MOODLE_501_STABLE
• master branch
• Any version with commit 7e07704 or later

References

• Regression introduced in: commit 7e07704 (March 18, 2026)
• Issue: User description field reset to '1' during every usersync
• User report: Description changes are not preserved during sync