function_exists() audit in wp-db.php

[johnjamesjacoby]

A few function_exists() checks can be removed from wp-db.php, thanks to recent load order changes, probably nobody having looked in a while, and generally being afraid to break DB drop-ins:

All of these functions are in files now loaded ahead of require_wp_db():

• is_multisite (load.php)
• _deprecated_function (functions.php)
• mb_strlen (compat.php)

Bonus:

• mb_check_encoding() could *maybe* be a new function in compat.php (it's used 3 times in core, using @ or function_exists)

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The only caveats are the installation process, and 10+ year-old HyperDB versions that do the old-school deep-integration thing, of directly including files – they'll need extra scrutiny.

[hellofromTonya]

Removing needs-testing until ticket is marked as needs-patch or has-patch.