[wp-trac] [WordPress Trac] #51988: Call to undefined function mysql_connect()

[WordPress Trac]

#51988: Call to undefined function mysql_connect()
-------------------------------------------------+-------------------------
 Reporter:  bgin                                 |       Owner:  (none)
     Type:  defect (bug)                         |      Status:  reopened
 Priority:  normal                               |   Milestone:  6.3
Component:  Database                             |     Version:  5.6
 Severity:  normal                               |  Resolution:
 Keywords:  php8 has-patch needs-testing has-    |     Focuses:
  testing-info                                   |
-------------------------------------------------+-------------------------
Changes (by SergeyBiryukov):

 * keywords:  php8 needs-patch => php8 has-patch needs-testing has-testing-
     info
 * milestone:  Future Release => 6.3


Comment:

 Replying to [comment:16 SergeyBiryukov]:
 > {{{
 > Fatal error: Uncaught Error: Call to undefined function mysql_connect()
 in wp-includes/class-wpdb.php:1963
 > }}}
 >
 > I was able to reproduce this error message by accidentally using a non-
 thread safe version of PHP as an Apache module, instead of the thread safe
 version recommended in that case.

 It appears that simply disabling the `mysqli` PHP extension on an existing
 installation has the same effect.

 [attachment:"51988.diff"] implements comment:17 and moves some
 conditionals around to simplify the logic and avoid repeating code. It
 turned out that `wpdb::bail()` would also need to check if `mysql_error()`
 exists to avoid a fatal error.

 Taking a step back though, it seems that checking for this in
 `wpdb::db_connect()` is perhaps a bit too late in the request, as we have
 a dedicated function, `wp_check_php_mysql_versions()`, which runs earlier
 on each request.

 In my testing, `wp_check_php_mysql_versions()` does not bail here due to
 the `extension_loaded( 'mysqlnd' )` check added in [36434] / #33261. The
 `mysqlnd` extension is reported as available on my environment, but does
 not appear to work as a fallback in case `mysqli` is not available, at
 least not on PHP 8.0+.

 So [attachment:"51988.alt.diff"] is an alternative patch which checks if
 either `mysqli_connect()` or `mysql_connect()` function exists, and
 returns early from `wp_check_php_mysql_versions()` otherwise with a more
 friendly message.

 To test:
 * Use PHP 8.0 or later.
 * Disable the `mysqli` extension on an existing WordPress installation.
 * You'll get a `Call to undefined function mysql_connect()` fatal error.

 With the patch (either of them), you'll get a message instead of a fatal
 error:
 > Your PHP installation appears to be missing the MySQL extension which is
 required by WordPress.
 >
 > Please check that the `mysqli` PHP extension is installed and enabled.
 >
 > If you are unsure what these terms mean you should probably contact your
 host. If you still need help you can always visit the
 [https://wordpress.org/support/forums/ WordPress Support Forums].

-- 
Ticket URL: <https://core.trac.wordpress.org/ticket/51988#comment:19>
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