spell: add GameTooltip:AddSpellByID(spellID)

Append counterpart to SetSpellByID -- adds a spell's tooltip (name, cast
time, cost, range, description) to the current tooltip WITHOUT clearing
existing lines, so callers can compose tooltips like
AddLine(header) + AddSpellByID(id).

BuildSpellTooltip's last arg gates the clear: SetSpellByID passes 0
(clears via FUN_00530050 first); AddSpellByID passes 1 (skips the clear
and appends). That append path is the engine's talent "next rank"
preview, so it emits a "Next rank:" header instead of the spell name and
doesn't stash the displayed spellID -- we overwrite that header line (at
the pre-build numLines index) with the real name from Spell.dbc and let
GetSpell keep reflecting the base tooltip. Verified in-game.

Author: brues-code

README.md

@@ -38,7 +38,7 @@ Full per-function reference: **[docs/API.md](docs/API.md)**.
 | [FriendList](docs/API.md#friendlist) | `C_FriendList.IsWhoQueryPending`, `C_FriendList.SendWhoQueryByName` |
 | [GameObject](docs/API.md#gameobject) | `C_GameObjectInfo.GetGameObjectInfoByID`, `C_GameObjectInfo.RequestLoadGameObjectByID`, `ClosestGameObjectPosition` |
 | [Gossip](docs/API.md#gossip) | `C_GossipInfo.CloseGossip`, `C_GossipInfo.GetActiveQuests`, `C_GossipInfo.GetAvailableQuests`, `C_GossipInfo.GetNumActiveQuests`, `C_GossipInfo.GetNumAvailableQuests`, `C_GossipInfo.GetNumOptions`, `C_GossipInfo.GetOptions`, `C_GossipInfo.GetText`, `C_GossipInfo.SelectActiveQuest`, `C_GossipInfo.SelectAvailableQuest`, `C_GossipInfo.SelectOption`, `C_GossipInfo.SelectOptionByIndex` |
-| [GameTooltip](docs/API.md#gametooltip) | `GameTooltip:GetGameObject`, `GameTooltip:GetItem`, `GameTooltip:GetOwner`, `GameTooltip:GetSpell`, `GameTooltip:GetUnitGUID`, `GameTooltip:HasGameObject`, `GameTooltip:HasItem`, `GameTooltip:HasSpell`, `GameTooltip:HasUnit`, `GameTooltip:IsEquippedItem`, `GameTooltip:SetEquipmentSet`, `GameTooltip:SetHyperlinkCompareItem`, `GameTooltip:SetInventoryItemByID`, `GameTooltip:SetItemByGUID`, `GameTooltip:SetItemByID`, `GameTooltip:SetSpellByID`, `GameTooltip:SetTalentByID`, `GameTooltip:SetUnitAura`, `OnTooltipSetItem` (script) |
+| [GameTooltip](docs/API.md#gametooltip) | `GameTooltip:AddSpellByID`, `GameTooltip:GetGameObject`, `GameTooltip:GetItem`, `GameTooltip:GetOwner`, `GameTooltip:GetSpell`, `GameTooltip:GetUnitGUID`, `GameTooltip:HasGameObject`, `GameTooltip:HasItem`, `GameTooltip:HasSpell`, `GameTooltip:HasUnit`, `GameTooltip:IsEquippedItem`, `GameTooltip:SetEquipmentSet`, `GameTooltip:SetHyperlinkCompareItem`, `GameTooltip:SetInventoryItemByID`, `GameTooltip:SetItemByGUID`, `GameTooltip:SetItemByID`, `GameTooltip:SetSpellByID`, `GameTooltip:SetTalentByID`, `GameTooltip:SetUnitAura`, `OnTooltipSetItem` (script) |
 | [Hooks](docs/API.md#hooks) | `hooksecurefunc` |
 | [Input](docs/API.md#input) | `GetMouseButtonClicked`, `IsLeftAltKeyDown`, `IsLeftControlKeyDown`, `IsLeftShiftKeyDown`, `IsModifierKeyDown`, `IsMouseButtonDown`, `IsRightAltKeyDown`, `IsRightControlKeyDown`, `IsRightShiftKeyDown` |
 | [Instance](docs/API.md#instance) | `GetInstanceInfo` |

docs/API.md

@@ -161,6 +161,7 @@ build instructions.
 
 - [GameTooltip](#gametooltip)
   - [`GameTooltip:SetSpellByID(spellID)`](#gametooltipsetspellbyidspellid)
+  - [`GameTooltip:AddSpellByID(spellID)`](#gametooltipaddspellbyidspellid)
   - [`GameTooltip:SetTalentByID(talentID)`](#gametooltipsettalentbyidtalentid)
   - [`GameTooltip:SetInventoryItemByID(itemID)`](#gametooltipsetinventoryitembyiditemid)
   - [`GameTooltip:SetHyperlinkCompareItem("itemLink" [, offset, shiftButton, comparisonTooltip])`](#gametooltipsethyperlinkcompareitemitemlink--offset-shiftbutton-comparisontooltip)
@@ -3787,6 +3788,32 @@ GameTooltip:SetSpellByID(133)  -- Fireball
 GameTooltip:Show()
 ```
 
+### `GameTooltip:AddSpellByID(spellID)`
+
+The append counterpart to [`SetSpellByID`](#gametooltipsetspellbyidspellid):
+adds a spell's full tooltip (name, cast time, cost, range, description) to
+the *current* tooltip **without clearing** the existing lines. Works for any
+`spellID`, learned or not. Lets you compose tooltips — e.g. a header line
+plus a spell block.
+
+```lua
+GameTooltip:SetOwner(UIParent, "ANCHOR_CURSOR")
+GameTooltip:AddLine("Rank 3 grants:")
+GameTooltip:AddSpellByID(133)  -- Fireball, appended below the header
+GameTooltip:Show()
+```
+
+Unlike `SetSpellByID`, this does **not** update what
+[`GetSpell`](#gametooltipgetspell) reports — the appended spell isn't the
+tooltip's "primary" spell, so `GetSpell` keeps reflecting whatever `SetX`
+call (if any) built the base tooltip. Silent no-op for `spellID <= 0` or an
+unknown spell.
+
+> Vanilla's tooltip builder only exposes "append" via its internal talent
+> "next rank" preview, which emits a `Next rank:` header instead of the
+> spell name; we overwrite that header line with the real name so the
+> appended block reads normally.
+
 ### `GameTooltip:GetItem()`
 
 Returns `(name, link, itemID)` for whichever item the tooltip is

src/spell/Tooltip.cpp

@@ -55,6 +55,71 @@ static int __fastcall Script_GameTooltipSetSpellByID(void *L) {
     return 0;
 }
 
+// `GameTooltip:AddSpellByID(spellID)` — APPENDS a spell's tooltip to the
+// current one instead of clearing+rebuilding (the `SetSpellByID` behavior).
+// The natural pair to `SetSpellByID`; lets callers compose tooltips like
+// `AddLine(talentName) + AddSpellByID(rankSpellID)`.
+//
+// `BuildSpellTooltip`'s last arg (`param_7`) gates the clear: `0` calls the
+// per-tooltip Clear (`FUN_00530050`) first — that's `SetSpellByID`; non-zero
+// SKIPS the clear and appends. The append path is the engine's talent
+// "next rank" preview, so it (a) emits a `"\nNext rank:"` header line
+// instead of the spell name, and (b) does NOT stash the displayed spellID at
+// `+0x39C` (so `GetSpell` keeps reflecting the base tooltip — correct for an
+// append). We fix (a) by overwriting that header line — which lands at index
+// `numLines`-before-the-build (0-based) — with the real spell name via the
+// line pool's left-text FontString. Verified against `FUN_0052E610`.
+void AppendByID(void *L, int spellID) {
+    if (spellID <= 0)
+        return;
+    void *tooltipObj = Game::Lua::ResolveObject(L, 1);
+    if (tooltipObj == nullptr)
+        return;
+    auto *tt = static_cast<uint8_t *>(tooltipObj);
+
+    const int before = *reinterpret_cast<const int *>(
+        tt + Offsets::OFF_GAMETOOLTIP_NUM_LINES);
+
+    auto BuildSpellTooltip =
+        reinterpret_cast<BuildSpellTooltip_t>(Offsets::FUN_GAMETOOLTIP_BUILD_SPELL_TOOLTIP);
+    BuildSpellTooltip(tooltipObj, spellID, 0, 0, 0, 0, 0, /*param_7 (append)=*/1);
+
+    const int after = *reinterpret_cast<const int *>(
+        tt + Offsets::OFF_GAMETOOLTIP_NUM_LINES);
+    if (after <= before)
+        return; // nothing appended (bad spellID / missing Spell.dbc record)
+
+    const uint8_t *record = Spell::Lookup::RecordForID(spellID);
+    if (record == nullptr)
+        return;
+    const int locale = *reinterpret_cast<const int *>(Offsets::VAR_LOCALE_INDEX);
+    const char *name = *reinterpret_cast<const char *const *>(
+        record + OFF_SPELL_NAME + locale * 4);
+    if (name == nullptr || name[0] == '\0')
+        return;
+
+    // Left-text FontString array: descriptor at +0x324, data ptr at +0x8.
+    auto **textLeft = *reinterpret_cast<void ***>(
+        tt + Offsets::OFF_GAMETOOLTIP_TEXTLEFT_DESC + 8);
+    if (textLeft == nullptr)
+        return;
+    void *fs = textLeft[before];
+    if (fs == nullptr)
+        return;
+    using SetText_t = void(__thiscall *)(void *fs, const char *text, int flag);
+    reinterpret_cast<SetText_t>(Offsets::FUN_FONTSTRING_SET_TEXT)(fs, name, 0);
+}
+
+static int __fastcall Script_GameTooltipAddSpellByID(void *L) {
+    if (Game::Lua::Type(L, 1) != Game::Lua::TYPE_TABLE ||
+        !Game::Lua::IsNumber(L, 2)) {
+        Game::Lua::Error(L, "Usage: GameTooltip:AddSpellByID(spellID)");
+        return 0;
+    }
+    AppendByID(L, static_cast<int>(Game::Lua::ToNumber(L, 2)));
+    return 0;
+}
+
 // `GameTooltip:GetSpell()` → (name, rank, spellID) for whichever spell
 // the tooltip is currently displaying, or nothing if it isn't showing
 // a spell. BuildSpellTooltip writes the spellID to `tooltip+0x39C`;
@@ -126,6 +191,7 @@ static int __fastcall Script_GameTooltipHasSpell(void *L) {
 
 static const Game::Lua::FrameMethodEntry g_methods[] = {
     {"SetSpellByID", &Script_GameTooltipSetSpellByID},
+    {"AddSpellByID", &Script_GameTooltipAddSpellByID},
     {"GetSpell", &Script_GameTooltipGetSpell},
     {"HasSpell", &Script_GameTooltipHasSpell},
 };

src/spell/Tooltip.h

@@ -26,4 +26,13 @@ namespace Spell::Tooltip {
 // so we render the rank-1 spell tooltip instead).
 void ShowByID(void *L, int spellID);
 
+// Like `ShowByID` but APPENDS the spell's tooltip to the current one
+// (no clear), and overwrites the engine's talent "next rank" header with
+// the real spell name. Backs `GameTooltip:AddSpellByID`. Silent no-op if
+// `spellID <= 0`, stack[1] isn't a frame object, or the build added no
+// lines. Does not stash the displayed spellID (so `GetSpell` still
+// reflects the base tooltip). Useful for cross-class talent tooltips
+// (`AddLine(talentName) + AppendByID(rankSpellID)`).
+void AppendByID(void *L, int spellID);
+
 } // namespace Spell::Tooltip