Core: Combat/threat system rewrite (PR #19930)

- PvE combat is now always mutual. UNIT_FLAG_IN_COMBAT is backed by actual references to the units we're in combat with.
- PvP combat is now also tracked, and almost always mutual; spells like Vanish and Feign Death can break this rule. That means we can easily determine a list of players we're fighting.
- By extension, IsInCombatWith now has sensible behavior when invoked on nonplayers.
- Threat and combat systems are no longer the same.
  - They still have an enforced relationship (threat implies combat - clearing combat clears threat)...
  - ...but we can have combat without threat. A creature (with threat list) isn't considered to be engaged until it has an entry on its threat list...
  - ...which means we can now faithfully replicate retail engage behavior. Combat on projectile launch - engagement start on projectile impact. Yay for progress!
- AI method refactor, as already ported in 6113b9d - `JustEngagedWith`, `JustEnteredCombat` and `JustExitedCombat`.
- Vehicle threat is now properly pooled on the main vehicle body (fixes #16542).
- Various edge case bug fixes for threat redirects (Misdirection "cancelling" Vigilance and similar).
- Target re-selection is now significantly faster.
- Fixed a ton of other smaller edge case bugs, probably.

Closes #7951 and #19998.

(cherry picked from commit 532ab1c7f8653d1a2e48aa1f1f8a9ba1041d4bb7)

1 files changed, 8 insertions, 3 deletions

diff --git a/src/server/game/Spells/Spell.cpp b/src/server/game/Spells/Spell.cpp
index 54cf9337114..8b0733a4b92 100644
--- a/src/server/game/Spells/Spell.cpp
+++ b/src/server/game/Spells/Spell.cpp
@@ -2560,7 +2560,7 @@ void Spell::DoAllEffectOnTarget(TargetInfo* target)
     // spellHitTarget can be null if spell is missed in DoSpellHitOnUnit
     if (missInfo != SPELL_MISS_EVADE && spellHitTarget && !m_caster->IsFriendlyTo(unit) && (!IsPositive() || m_spellInfo->HasEffect(SPELL_EFFECT_DISPEL)))
     {
-        m_caster->CombatStart(unit, m_spellInfo->HasInitialAggro());
+        m_caster->AttackedTarget(unit, m_spellInfo->HasInitialAggro());
 
         if (!unit->IsStandState())
             unit->SetStandState(UNIT_STAND_STATE_STAND);
@@ -2655,7 +2655,8 @@ SpellMissInfo Spell::DoSpellHitOnUnit(Unit* unit, uint32 effectMask)
             }
             if (unit->IsInCombat() && m_spellInfo->HasInitialAggro())
             {
-                m_caster->SetInCombatState(unit->GetCombatTimer() > 0, unit);
+                if (m_caster->HasUnitFlag(UNIT_FLAG_PVP_ATTACKABLE))               // only do explicit combat forwarding for PvP enabled units
+                    m_caster->GetCombatManager().InheritCombatStatesFrom(unit);    // for creature v creature combat, the threat forward does it for us
                 unit->GetThreatManager().ForwardThreatForAssistingMe(m_caster, 0.0f, nullptr, true);
             }
         }
@@ -7459,6 +7460,10 @@ void Spell::DoAllEffectOnLaunchTarget(TargetInfo& targetInfo, float* multiplier)
     if (!unit)
         return;
 
+    // This will only cause combat - the target will engage once the projectile hits (in DoAllEffectOnTarget)
+    if (targetInfo.missCondition != SPELL_MISS_EVADE && !m_caster->IsFriendlyTo(unit) && (!m_spellInfo->IsPositive() || m_spellInfo->HasEffect(SPELL_EFFECT_DISPEL)) && (m_spellInfo->HasInitialAggro() || unit->IsEngaged()))
+        m_caster->SetInCombatWith(unit);
+
     for (SpellEffectInfo const* effect : m_spellInfo->GetEffects())
     {
         if (effect && (targetInfo.effectMask & (1<<effect->EffectIndex)))
@@ -8043,7 +8048,7 @@ bool WorldObjectSpellTargetCheck::operator()(WorldObject* target)
                     return false;
                 break;
             case TARGET_CHECK_THREAT:
-                if (_referer->GetThreatManager().getThreat(unitTarget, true) <= 0.0f)
+                if (_referer->GetThreatManager().GetThreat(unitTarget, true) <= 0.0f)
                     return false;
                 break;
             case TARGET_CHECK_TAP: