Nickname your Pokémon from the party menu

In Pokémon Let's Go, Pikachu/Eevee, you can nickname your Pokémon from the party menu. Let's implement that feature into pokeemerald!

In include/strings.h:

  extern const u8 gText_Speed[];
  extern const u8 gText_Dash[];
  extern const u8 gText_Plus[];
+ extern const u8 gText_Nickname[];

  //pokedex text
  extern const u8 gText_CryOf[];

In src/data/party_menu.h:

enum
{
    MENU_SUMMARY,
+   MENU_NICKNAME,
    MENU_SWITCH,
    MENU_CANCEL1,
    MENU_ITEM,

} static const sCursorOptions[] =
{
    [MENU_SUMMARY] = {gText_Summary5, CursorCb_Summary},
+   [MENU_NICKNAME] = {gText_Nickname, CursorCb_Nickname},
    [MENU_SWITCH] = {gText_Switch2, CursorCb_Switch},
    [MENU_CANCEL1] = {gText_Cancel2, CursorCb_Cancel1},
    [MENU_ITEM] = {gText_Item, CursorCb_Item},

In src/party_menu.c:

  static void BlitBitmapToPartyWindow_LeftColumn(u8, u8, u8, u8, u8, u8);
  static void BlitBitmapToPartyWindow_RightColumn(u8, u8, u8, u8, u8, u8);
  static void CursorCb_Summary(u8);
+ static void CursorCb_Nickname(u8);
  static void CursorCb_Switch(u8);
  static void CursorCb_Cancel1(u8);
  static void CursorCb_Item(u8);

sPartyMenuInternal->numActions = 0;
    AppendToList(sPartyMenuInternal->actions, &sPartyMenuInternal->numActions, MENU_SUMMARY);
+   AppendToList(sPartyMenuInternal->actions, &sPartyMenuInternal->numActions, MENU_NICKNAME);

    // Add field moves to action list
    for (i = 0; i < MAX_MON_MOVES; i++)

     Task_ClosePartyMenu(taskId);
}

+ void ChangePokemonNickname(void);
+ static void CursorCb_Nickname(u8 taskId)
+ {
+     PlaySE(SE_SELECT);
+     gSpecialVar_0x8004 = gPartyMenu.slotId;
+     sPartyMenuInternal->exitCallback = ChangePokemonNickname;
+     Task_ClosePartyMenu(taskId);
+ }
+    
static void CB2_ShowPokemonSummaryScreen(void)
{
    if (gPartyMenu.menuType == PARTY_MENU_TYPE_IN_BATTLE)

In src/party_menu.c:

Around Line 125:

- u8 actions[8];
+ u8 actions [9];

Finally, in src/strings.c:

const u8 gText_PokeBalls[] = _("POKé BALLS");
const u8 gText_Berry[] = _("BERRY");
const u8 gText_Berries[] = _("BERRIES");
+ const u8 gText_Nickname[] = _("NICKNAME");
+     

Optional additions:

Technically, you could stop here. But there are a few changes you can make to this feature that will make it better:

Make it exit to the party screen

This is a pretty simple change, and it makes the experience way better.

In src/party_menu.c:

 #include "constants/party_menu.h"
 #include "constants/rgb.h"
 #include "constants/songs.h"
+#include "naming_screen.h"

 
 #define PARTY_PAL_SELECTED     (1 << 0)
 #define PARTY_PAL_FAINTED      (1 << 1)

     Task_ClosePartyMenu(taskId);
 }
 
-void ChangePokemonNickname(void);
+static void ChangePokemonNicknamePartyScreen_CB(void)
+{
+    SetMonData(&gPlayerParty[gSpecialVar_0x8004], MON_DATA_NICKNAME, gStringVar2);
+    CB2_ReturnToPartyMenuFromSummaryScreen();
+}
+
+static void ChangePokemonNicknamePartyScreen(void)
+{
+    GetMonData(&gPlayerParty[gSpecialVar_0x8004], MON_DATA_NICKNAME, gStringVar3);
+    GetMonData(&gPlayerParty[gSpecialVar_0x8004], MON_DATA_NICKNAME, gStringVar2);
+    DoNamingScreen(NAMING_SCREEN_NICKNAME, gStringVar2, GetMonData(&gPlayerParty[gSpecialVar_0x8004], MON_DATA_SPECIES, NULL), GetMonGender(&gPlayerParty[gSpecialVar_0x8004]), GetMonData(&gPlayerParty[gSpecialVar_0x8004], MON_DATA_PERSONALITY, NULL), ChangePokemonNicknamePartyScreen_CB);
+}
+
 static void CursorCb_Nickname(u8 taskId)
 {
     PlaySE(SE_SELECT);
     gSpecialVar_0x8004 = gPartyMenu.slotId;
-    sPartyMenuInternal->exitCallback = ChangePokemonNickname;
+    sPartyMenuInternal->exitCallback = ChangePokemonNicknamePartyScreen;
     Task_ClosePartyMenu(taskId);
 }