Monsters do abjuration instead of summoning in summon spells

[petzl]

Sorry if this has been asked and answered previously, but I notice that in the code,
many of the monster-initiated Summon spells have a 50% chance of doing a Mass Abjuration instead
of doing the original Summon spell (if there are player's summoned monsters about).

So, er, why?

From mon-cast.cc:2963:

  Code:

   case SPELL_SUMMON_DEMON: // class 2-4 demons
        if (_mons_abjured(mons, monsterNearby))
            return;

        sumcount2 = 1 + random2(mons->hit_dice / 10 + 1);

        duration  = std::min(2 + mons->hit_dice / 10, 6);
        for (sumcount = 0; sumcount < sumcount2; sumcount++)
        {
            create_monster(
                mgen_data(summon_any_demon(DEMON_COMMON),
                          SAME_ATTITUDE(mons), mons, duration, spell_cast,
                          mons->pos(), mons->foe, 0, god));
        }
        return;


[KoboldLord]

Probably the original reason is to prevent the player from simply flooding all valid grid spaces with butterflies, preventing the monsters from ever successfully summoning. 1mp would successfully shut down all summoners in the entire game, period.

It was never changed because summoning is still super-overpowered even with the inconvenience of monster abjuration.

[mageykun]

It's actually a case of player / monster symmetry, if you think about it. What's a player summoner's response to enemy summons? Kill 'em with your own, and/or abjure them. Perfectly reasonable, really.