Name a FireRed egg by the language's own EGG

Party.giveMon stores "EGG" as a new egg's nickname (party.lua for a
gift egg, breeding.lua for the Day-Care's), and the party slots and the
other screens that name a mon through Pokemon.displayName and
displayMonName print that nickname as it is. A translated game therefore
listed its eggs as EGG, while the summary, which prints Strings("EGG")
for an egg, already said OEUF, EI, HUEVO or UOVO.

The cart does not rely on the stored nickname either: its Day-Care
writes the Japanese タマゴ there (daycare.c:1100), and GetMonData
returns gText_EggNickname for any egg's nickname (pokemon.c:3020). Do the
same in both name helpers: an egg reads as Strings("EGG"), whatever its
nickname holds, which also covers the eggs saves already carry. A
hatched egg, whose nickname is cleared, goes back to its species name.

src/core/game3/pokemon.lua

@@ -1160,8 +1160,18 @@ function Pokemon.replaceMove(mon, slot, newMoveId)
   return old
 end
 
+-- An egg reads as the language's own EGG whatever its nickname holds: pret's
+-- GetMonData(MON_DATA_NICKNAME) returns gText_EggNickname for any egg
+-- (pokefirered/src/pokemon.c:3020).  The stored nickname is only a placeholder
+-- -- the cart's daycare writes タマゴ (daycare.c:1100), this engine "EGG".
+local function eggName(mon)
+  if Pokemon.isEgg(mon) then return Strings("EGG") end
+end
+
 function Pokemon.displayMonName(mon)
   if not mon then return "POKéMON" end
+  local egg = eggName(mon)
+  if egg then return egg end
   local nick = mon.nickname
   if type(nick) == "string" and nick ~= "" then return nick end
   if mon.name and mon.name ~= "" then return mon.name end
@@ -1572,6 +1582,8 @@ end
 
 function Pokemon.displayName(mon)
   if not mon then return "?????" end
+  local egg = eggName(mon)
+  if egg then return egg end
   if mon.nickname and mon.nickname ~= "" then return tostring(mon.nickname) end
   -- Prefer pack name over host species string when we can resolve.
   local sp = Pokemon.speciesOf(mon)

tests/engine/game3_egg_display_name_test.lua

@@ -0,0 +1,44 @@
+#!/usr/bin/env luajit
+-- An egg is named by the language's own EGG, as pret's GetMonData(MON_DATA_NICKNAME)
+-- does for any egg (pokefirered/src/pokemon.c:3020): the party and every screen
+-- that names a mon through Pokemon.displayName / displayMonName show it, whatever
+-- placeholder the egg's nickname stores.
+
+package.path = "./?.lua;./?/init.lua;" .. package.path
+love = require("tests.love_stub")
+
+local T = require("tests.harness")
+local check = T.check
+
+local Strings = require("src.core.Strings")
+local Pokemon = require("src.core.game3.pokemon")
+
+-- A minimal pack, so no ROM is needed.
+Pokemon._names = { [25] = "PIKACHU", [172] = "PICHU" }
+
+local egg = { species = 172, isEgg = true, nickname = "EGG", name = "EGG" }
+local hatched = { species = 172, isEgg = false, nickname = "", name = "PICHU" }
+local named = { species = 25, nickname = "SPARKY" }
+
+Strings.load({})
+check(Pokemon.displayName(egg) == "EGG", "an egg reads EGG with no catalog")
+check(Pokemon.displayMonName(egg) == "EGG", "in both name helpers")
+
+Strings.load({ strings = { EGG = "OEUF" } })
+check(Pokemon.displayName(egg) == "OEUF", "an egg follows the catalog's EGG")
+check(Pokemon.displayMonName(egg) == "OEUF", "in both name helpers")
+check(egg.nickname == "EGG", "without its stored nickname being rewritten")
+
+local bare = { species = 172, isEgg = true, nickname = "" }
+check(Pokemon.displayName(bare) == "OEUF", "an egg with no nickname at all is still named EGG")
+local species_only = { species = 412, nickname = "" }
+check(Pokemon.displayName(species_only) == "OEUF", "and so is one known only by the egg species")
+
+-- (looking up a species the pack lacks reloads it; put the minimal one back)
+Pokemon._names = { [25] = "PIKACHU", [172] = "PICHU" }
+check(Pokemon.displayName(hatched) == "PICHU", "a hatched egg goes back to its species name")
+check(Pokemon.displayName(named) == "SPARKY", "and a nicknamed mon keeps its nickname")
+check(Pokemon.displayMonName(named) == "SPARKY", "in both name helpers")
+
+Strings.load({})
+T.finish("game3_egg_display_name_test")