[3.0] Restores the strings the backup checkbox explains itself with

[albertlast]

Description

The line of help text under the "Backup SMF tables" checkbox on the upgrader's options page is empty, whichever of its two states it is in.

UpgradeTemplate.php picks one of two strings for it:

<span class="smalltext">', Lang::getTxt(empty(Utils::$context['backup_recommended']) ? 'upgrade_backup_already_exists' : 'upgrade_recommended', file: 'Maintenance'), '</span>

Neither is defined. ddb7919c1 ("Cleans up maintenance strings") removed both from Languages/en_US/Maintenance.php and left the two call sites behind:

-$txt['upgrade_recommended'] = 'Strongly recommended!';
-$txt['upgrade_backup_already_exists'] = 'Backup already exists. If you enable this option, the existing backup will be replaced with a new one.';

Nothing reports it, because Lang::getTxt() ends with

return self::${$var}[$txt_key[0]] ?? '';

A key that does not exist is an empty string, not a missing-string marker, so the page renders <span class="smalltext"></span> and looks like a design choice rather than a fault.

The second of the two is the one worth having back. doBackupTable() calls Db::$db->backup_table(), which drops the destination table before writing it, so ticking that box when a backup is already there replaces it with a copy of the database as it stands now. That sentence is the only place the admin is told so.

This restores both strings as they were.

How this was verified

First statically: every string literal that UpgradeTemplate.php passes as the first argument to getTxt(), checked against every $txt, $helptxt, $tztxt, $editortxt and $txtBirthdayEmails key defined anywhere in Languages/en_US/. Of the 65 language keys the template uses, these two are the only ones with no definition.

Then on the page itself, against a 2.1.7 baseline upgraded to 3.0 so that a full set of backup_ tables exists, reading the rendered span on step 2:

backup_recommended	before	after
false — a backup already exists	<span class="smalltext"></span>	Backup already exists. If you enable this option, the existing backup will be replaced with a new one.
true — none does, or the upgrade is unfinished	<span class="smalltext"></span>	Strongly recommended!

Both branches were reached on a running forum rather than reasoned about: the first as the upgrade left it, the second by putting smfVersion back to 2.1.7 so backupRecommended() takes the other path, and restoring it afterwards.

Not reachable from the unit suite

The strings are read by a template that renders a page, and beStrictAboutOutputDuringTests means the suite cannot run one.

Issues References (Fixes|Related|Closes)

1. Related: [3.0] Documents what a schema migration has to prove before it is safe #9617, which documents what an interrupted upgrade does to the backup this text is about.