Core/Spells: implement SpellInfo helper to filter for relevant mechanic immunities in spell_start packet (#26183)

* Core/Spells: implement SpellInfo helper to filter for relevant mechanic immunities when sending SMSG_SPELL_START packets.

According to sniff analysis Blizzard does not send all mechanic immunities of creatures but instead only the ones that are responsible for actual interrupts which are MECHANIC_INTERRUPT  and MECHANIC_SILENCE. Additionally we no longer send immunities for instant cast spells as sniffs confirm that they are not sent for spells without a cast time.

(cherry picked from commit 6215cb4e0014fbe9df35a8c6b013e7801bd8ffec)

3 files changed, 25 insertions, 6 deletions

diff --git a/src/server/game/Spells/Spell.cpp b/src/server/game/Spells/Spell.cpp
index 39eb1867b65..6adbfa28086 100644
--- a/src/server/game/Spells/Spell.cpp
+++ b/src/server/game/Spells/Spell.cpp
@@ -4469,8 +4469,8 @@ void Spell::SendSpellStart()
     uint32 mechanicImmunityMask = 0;
     if (Unit* unitCaster = m_caster->ToUnit())
     {
-        schoolImmunityMask = unitCaster->GetSchoolImmunityMask();
-        mechanicImmunityMask = unitCaster->GetMechanicImmunityMask();
+        schoolImmunityMask = m_timer!= 0 ? unitCaster->GetSchoolImmunityMask() : 0;
+        mechanicImmunityMask = m_timer != 0 ? m_spellInfo->GetMechanicImmunityMask(unitCaster) : 0;
     }
 
     if (schoolImmunityMask || mechanicImmunityMask)
diff --git a/src/server/game/Spells/SpellInfo.cpp b/src/server/game/Spells/SpellInfo.cpp
index 8f799d9422a..9c089aacd74 100644
--- a/src/server/game/Spells/SpellInfo.cpp
+++ b/src/server/game/Spells/SpellInfo.cpp
@@ -1376,14 +1376,14 @@ bool SpellInfo::HasTargetType(::Targets target) const
     return false;
 }
 
-bool SpellInfo::CanBeInterrupted(WorldObject const* interruptCaster, Unit const* interruptTarget) const
+bool SpellInfo::CanBeInterrupted(WorldObject const* interruptCaster, Unit const* interruptTarget, bool ignoreImmunity /*= false*/) const
 {
     return HasAttribute(SPELL_ATTR7_CAN_ALWAYS_BE_INTERRUPTED)
         || HasChannelInterruptFlag(SpellAuraInterruptFlags::Damage | SpellAuraInterruptFlags::EnteringCombat)
         || (interruptTarget->IsPlayer() && InterruptFlags.HasFlag(SpellInterruptFlags::DamageCancelsPlayerOnly))
         || InterruptFlags.HasFlag(SpellInterruptFlags::DamageCancels)
-        || (interruptCaster->IsUnit() && interruptCaster->ToUnit()->HasAuraTypeWithMiscvalue(SPELL_AURA_ALLOW_INTERRUPT_SPELL, Id))
-        || (!(interruptTarget->GetMechanicImmunityMask() & (1 << MECHANIC_INTERRUPT))
+        || (interruptCaster && interruptCaster->IsUnit() && interruptCaster->ToUnit()->HasAuraTypeWithMiscvalue(SPELL_AURA_ALLOW_INTERRUPT_SPELL, Id))
+        || ((!(interruptTarget->GetMechanicImmunityMask() & (1 << MECHANIC_INTERRUPT)) || ignoreImmunity)
             && !interruptTarget->HasAuraTypeWithAffectMask(SPELL_AURA_PREVENT_INTERRUPT, this)
             && PreventionType & SPELL_PREVENTION_TYPE_SILENCE);
 }
@@ -3729,6 +3729,23 @@ uint32 SpellInfo::GetAllowedMechanicMask() const
     return _allowedMechanicMask;
 }
 
+uint32 SpellInfo::GetMechanicImmunityMask(Unit const* caster) const
+{
+    uint32 casterMechanicImmunityMask = caster->GetMechanicImmunityMask();
+    uint32 mechanicImmunityMask = 0;
+
+    if (CanBeInterrupted(nullptr, caster, true))
+    {
+        if (casterMechanicImmunityMask & (1 << MECHANIC_SILENCE))
+            mechanicImmunityMask |= (1 << MECHANIC_SILENCE);
+
+        if (casterMechanicImmunityMask & (1 << MECHANIC_INTERRUPT))
+            mechanicImmunityMask |= (1 << MECHANIC_INTERRUPT);
+    }
+
+    return mechanicImmunityMask;
+}
+
 float SpellInfo::GetMinRange(bool positive /*= false*/) const
 {
     if (!RangeEntry)
diff --git a/src/server/game/Spells/SpellInfo.h b/src/server/game/Spells/SpellInfo.h
index 21425d1b595..bb4c11871f4 100644
--- a/src/server/game/Spells/SpellInfo.h
+++ b/src/server/game/Spells/SpellInfo.h
@@ -476,7 +476,7 @@ class TC_GAME_API SpellInfo
         bool HasAttribute(SpellAttr14 attribute) const { return !!(AttributesEx14 & attribute); }
         bool HasAttribute(SpellCustomAttributes customAttribute) const { return !!(AttributesCu & customAttribute); }
 
-        bool CanBeInterrupted(WorldObject const* interruptCaster, Unit const* interruptTarget) const;
+        bool CanBeInterrupted(WorldObject const* interruptCaster, Unit const* interruptTarget, bool ignoreImmunity = false) const;
 
         bool HasAnyAuraInterruptFlag() const;
         bool HasAuraInterruptFlag(SpellAuraInterruptFlags flag) const { return AuraInterruptFlags.HasFlag(flag); }
@@ -605,6 +605,8 @@ class TC_GAME_API SpellInfo
 
         uint32 GetAllowedMechanicMask() const;
 
+        uint32 GetMechanicImmunityMask(Unit const* caster) const;
+
         // Player Condition
         bool MeetsFutureSpellPlayerCondition(Player const* player) const;