Core/Spell: partial revert of SPELL_ATTR1_UNAFFECTED_BY_SCHOOL_IMMUNE immunity handling

- Bonus: without breaking Banish... yay!
Closes #18370
(cherry picked from commit 560c882b364630bf95e1c6859ceaa6fa3cb6ed2e)

2 files changed, 19 insertions, 11 deletions

diff --git a/src/server/game/Entities/Unit/Unit.cpp b/src/server/game/Entities/Unit/Unit.cpp
index 381ab4f2f45..9d209ba9550 100644
--- a/src/server/game/Entities/Unit/Unit.cpp
+++ b/src/server/game/Entities/Unit/Unit.cpp
@@ -7167,7 +7167,7 @@ bool Unit::IsImmunedToSpell(SpellInfo const* spellInfo, Unit* caster) const
     {
         // State/effect immunities applied by aura expect full spell immunity
         // Ignore effects with mechanic, they are supposed to be checked separately
-        if (!effect)
+        if (!effect || !effect->IsEffect())
             continue;
         if (!IsImmunedToSpellEffect(spellInfo, effect->EffectIndex, caster))
         {
@@ -7179,17 +7179,14 @@ bool Unit::IsImmunedToSpell(SpellInfo const* spellInfo, Unit* caster) const
     if (immuneToAllEffects) //Return immune only if the target is immune to all spell effects.
         return true;
 
-    if (!spellInfo->HasAttribute(SPELL_ATTR1_UNAFFECTED_BY_SCHOOL_IMMUNE) && !spellInfo->HasAttribute(SPELL_ATTR2_UNAFFECTED_BY_AURA_SCHOOL_IMMUNE))
+    SpellImmuneContainer const& schoolList = m_spellImmune[IMMUNITY_SCHOOL];
+    for (auto itr = schoolList.begin(); itr != schoolList.end(); ++itr)
     {
-        SpellImmuneContainer const& schoolList = m_spellImmune[IMMUNITY_SCHOOL];
-        for (auto itr = schoolList.begin(); itr != schoolList.end(); ++itr)
-        {
-            SpellInfo const* immuneSpellInfo = sSpellMgr->GetSpellInfo(itr->second);
-            if ((itr->first & spellInfo->GetSchoolMask())
-                && !(immuneSpellInfo && immuneSpellInfo->IsPositive() && spellInfo->IsPositive() && IsFriendlyTo(caster))
-                && !spellInfo->CanPierceImmuneAura(immuneSpellInfo))
-                return true;
-        }
+        SpellInfo const* immuneSpellInfo = sSpellMgr->GetSpellInfo(itr->second);
+        if ((itr->first & spellInfo->GetSchoolMask())
+            && !(immuneSpellInfo && immuneSpellInfo->IsPositive() && spellInfo->IsPositive() && IsFriendlyTo(caster))
+            && !spellInfo->CanPierceImmuneAura(immuneSpellInfo))
+            return true;
     }
 
     return false;
diff --git a/src/server/game/Spells/SpellInfo.cpp b/src/server/game/Spells/SpellInfo.cpp
index 1cbf291c164..9d51d735e38 100644
--- a/src/server/game/Spells/SpellInfo.cpp
+++ b/src/server/game/Spells/SpellInfo.cpp
@@ -1615,6 +1615,17 @@ bool SpellInfo::CanPierceImmuneAura(SpellInfo const* auraSpellInfo) const
     if (HasAttribute(SPELL_ATTR0_UNAFFECTED_BY_INVULNERABILITY))
         return true;
 
+    // these spells (Cyclone for example) can pierce all...
+    if (HasAttribute(SPELL_ATTR1_UNAFFECTED_BY_SCHOOL_IMMUNE) || HasAttribute(SPELL_ATTR2_UNAFFECTED_BY_AURA_SCHOOL_IMMUNE))
+    {
+        // ...but not these (Divine shield, Ice block, Cyclone and Banish for example)
+        if (!auraSpellInfo ||
+            (auraSpellInfo->Mechanic != MECHANIC_IMMUNE_SHIELD &&
+                auraSpellInfo->Mechanic != MECHANIC_INVULNERABILITY &&
+                (auraSpellInfo->Mechanic != MECHANIC_BANISH || IsRankOf(auraSpellInfo)))) // Banish shouldn't be immune to itself
+            return true;
+    }
+
     // Dispels other auras on immunity, check if this spell makes the unit immune to aura
     if (HasAttribute(SPELL_ATTR1_DISPEL_AURAS_ON_IMMUNITY) && CanSpellProvideImmunityAgainstAura(auraSpellInfo))
         return true;