Feat warcaster spell attack question

[Whit]

1. When a hostile creature’s movement provokes an opportunity attack from you, you can use your reaction to cast a spell at the creature, rather than making an opportunity attack. The spell must have a casting time of 1 action and must target only that creature.

Question If I use a spell attack, am I now going to suffer page 205 disadvantage when casting an attack spell on a target within 5ft. or does warcaster cancel it.

[JNAProductions]

You would have disadvantage, unless it was a melee spell attack or you have Crossbow Expert.

[Expired]

1. When a hostile creature’s movement provokes an opportunity attack from you, you can use your reaction to cast a spell at the creature, rather than making an opportunity attack. The spell must have a casting time of 1 action and must target only that creature.

Question If I use a spell attack, am I now going to suffer page 205 disadvantage when casting an attack spell on a target within 5ft. or does warcaster cancel it.

The attack of opportunity occurs while the target is still within your reach (5ft), so any ranged attack and/or ranged spell attack would roll with disadvantage--unless you also have the Crossbow Expert feat. Link to a forum post explaining this (https://rpg.stackexchange.com/questions/86985/does-the-warcaster-feat-grant-ranged-spell-attacks-in-melee-range-without-disadv).

[Mr Adventurer]

You could also cast a spell that doesn't have an attack roll to avoid this.

[Greywander]

Yes, a ranged attack (including ranged spell attacks) will have disadvantage due to being in melee range, unless you have the Crossbow Expert feat (and yes, that feat works for spells, too).

Here's a few ways you can get around the disadvantage:

Get Crossbow Expert (as mentioned). This removes disadvantage from ranged attack made in melee range, including ranged spell attacks.
Use a spell with a melee spell attack.
Use a spell that doesn't use an attack roll (e.g. one that uses a saving throw).
Use Booming Blade. Note that this won't trigger the speed reduction from the Sentinel feat, as it isn't technically an OA anymore, even though it's a weapon attack.

Each of these works better for different builds. Gishs, or just straight up martials with a bit of magic, benefit most from using Booming Blade since they're already built around weapon attacks. Casters less so, so they tend to benefit more from the other three. With limited cantrip slots, it's often more economical to get a save cantrip that can be used at either melee or ranged, but a wizard or chainlock might want something like Shocking Grasp that can be delivered through a familiar. Thorn Whip is also an interesting one, as it's a melee attack with a 30 foot range. I'd wouldn't recommend Crossbow Expert if you're only getting it to remove disadvantage from ranged spell attacks, but if you're already rapid-firing a hand crossbow and want to sling spells, then go for it.

[Garfunion]

Also with the wording of the feat, you can use spells like magic missile or scorching ray on the triggering creature. As long as all the rays and bolts target the triggering creature.