Excerpt from mangos SpellMgr.cpp

SpellMgr-excerpt.cpp

bool SpellMgr::IsNoStackSpellDueToSpell(uint32 spellId_1, uint32 spellId_2) const
{
    SpellEntry const *spellInfo_1 = sSpellStore.LookupEntry(spellId_1);
    SpellEntry const *spellInfo_2 = sSpellStore.LookupEntry(spellId_2);

    if (!spellInfo_1 || !spellInfo_2)
        return false;

    if (spellId_1 == spellId_2)
        return false;

    // Resurrection sickness
    if ((spellInfo_1->Id == SPELL_ID_PASSIVE_RESURRECTION_SICKNESS) != (spellInfo_2->Id==SPELL_ID_PASSIVE_RESURRECTION_SICKNESS))
        return false;

    // Allow stack passive and not passive spells
    if (spellInfo_1->HasAttribute(SPELL_ATTR_PASSIVE) != spellInfo_2->HasAttribute(SPELL_ATTR_PASSIVE))
        return false;

    // Specific spell family spells
    switch(spellInfo_1->SpellFamilyName)
    {
        case SPELLFAMILY_GENERIC:
            switch(spellInfo_2->SpellFamilyName)
            {
                case SPELLFAMILY_GENERIC:                   // same family case
                {
                    // Thunderfury
                    if ((spellInfo_1->Id == 21992 && spellInfo_2->Id == 27648) ||
                        (spellInfo_2->Id == 21992 && spellInfo_1->Id == 27648))
                        return false;

                    // Lightning Speed (Mongoose) and Fury of the Crashing Waves (Tsunami Talisman)
                    if ((spellInfo_1->Id == 28093 && spellInfo_2->Id == 42084) ||
                        (spellInfo_2->Id == 28093 && spellInfo_1->Id == 42084))
                        return false;

                    // Soulstone Resurrection and Twisting Nether (resurrector)
                    if (spellInfo_1->SpellIconID == 92 && spellInfo_2->SpellIconID == 92 && (
                        (spellInfo_1->SpellVisual[0] == 99 && spellInfo_2->SpellVisual[0] == 0) ||
                        (spellInfo_2->SpellVisual[0] == 99 && spellInfo_1->SpellVisual[0] == 0)))
                        return false;

                    // Heart of the Wild, Agility and various Idol Triggers
                    if (spellInfo_1->SpellIconID == 240 && spellInfo_2->SpellIconID == 240)
                        return false;

                    // Personalized Weather (thunder effect should overwrite rainy aura)
                    if (spellInfo_1->SpellIconID == 2606 && spellInfo_2->SpellIconID == 2606)
                        return false;

                    // Mirrored Soul (FoS - Devourer) - and other Boss spells
                    if (spellInfo_1->SpellIconID == 3176 && spellInfo_2->SpellIconID == 3176)
                        return false;