The bug

Giving yourself weakness now negates only your weapon's base attack damage and not Sharpness/Smite/Bane of Arthropods damage.

How to reproduce

1. Run:

   /give @s splash_potion[minecraft:potion_contents={potion:"minecraft:long_weakness"}]
   /give @s diamond_hoe[minecraft:enchantments={"minecraft:sharpness":1}]
   /summon villager ~ ~ ~ {Health:1}

   → Observe how the diamond hoe's tooltip says 2 Attack Damage (or rather, imagine that it says that until MC-271840 is fixed) and the weakness potion's tooltip says -4 Attack Damage.

2. Throw the potion at your feet and hit the villager with the diamond hoe.
   → Villager died even though the potion was supposed to take away 4 (of your 2) attack damage

Notes

When attacking while falling, neither critical strike damage nor bonus damage from the mace are considered part of the base attack value (from which the weakness value is subtracted). However, if the attack manages to overcome the weakness value due to this bug, mace bonus damage will be applied while critical strike damage will not.