fix(gen2): honor mod move-grid navigation

docs/mod-api-gen2-compat.md

@@ -540,8 +540,9 @@ gains a field instead of the name gaining a prefix.
   `battle.crit`, `battle.accuracy`, `battle.turn_order`,
   `battle.enemy_action`, `battle.run`, `battle.exp_award`, `exp.gain`,
   `catch.rate`, `trainer.party`, `battle.overlay`, `battle.low_health_alarm`,
-  `battle.catch_exp`, `battle.bottom_ui_visible` and
-  `battle.status_hud_visible`. One payload difference: Gen 1's vanilla
+  `battle.catch_exp`, `battle.bottom_ui_visible`,
+  `battle.status_hud_visible` and `battle.move_grid_navigation`. One payload
+  difference: Gen 1's vanilla
   `battle.low_health_alarm` link reads `ctx.battle.data`, and Gold's battle
   screen has no `.data` field, so the Gen 2 site **adds** `ctx.data` beside the
   Gen 1 keys. A mod that calls `nextFn` is unaffected; one that reaches through

src/ui/gen2/BattleState.lua

@@ -44,6 +44,12 @@ local BattleState = {}
 BattleState.__index = BattleState
 BattleState.isOpaque = true
 
+function BattleState:moveGridNavigation()
+  if not Runtime.wantsHook("battle.move_grid_navigation") then return false end
+  return Runtime.call("battle.move_grid_navigation", function() return false end,
+                      self) == true
+end
+
 -- Armed while a battle line waits for PromptButton (home/text.asm).  Any
 -- positive value means "hold until A/B"; the cart never times these out, so
 -- the victory jingle can keep looping through the post-win prompts.
@@ -2043,7 +2049,22 @@ function BattleState:update(_dt)
 
   if self.phase == "moves" then
     local moves = self:playerMoves()
-    if input:wasPressed("up") then
+    local grid
+    if self:moveGridNavigation() then
+      local index, count = self.moveIndex, #moves
+      if input:wasPressed("left") or input:wasPressed("right") then
+        local other = math.floor((index - 1) / 2) * 2
+          + (1 - (index - 1) % 2) + 1
+        grid = other <= count and other or index
+      elseif input:wasPressed("up") or input:wasPressed("down") then
+        local other = (1 - math.floor((index - 1) / 2)) * 2
+          + (index - 1) % 2 + 1
+        grid = other <= count and other or index
+      end
+    end
+    if grid then
+      self.moveIndex = grid
+    elseif input:wasPressed("up") then
       self.moveIndex = self.moveIndex > 1 and self.moveIndex - 1 or #moves
     elseif input:wasPressed("down") then
       self.moveIndex = self.moveIndex < #moves and self.moveIndex + 1 or 1

tests/engine/gate_gen2_mod_api.lua

@@ -421,6 +421,7 @@ local GEN2_HOOKS = {
   -- nextFn gets nil there).
   "battle.catch_exp", "battle.low_health_alarm", "battle.overlay",
   "battle.bottom_ui_visible", "battle.status_hud_visible",
+  "battle.move_grid_navigation",
   -- One pic path resolver for both games: the Gen 1 site is the SHARED
   -- src/pokemon/Sprites.lua and Gold's own battle screen calls the same hook
   -- with the Gen 1 ctx keys plus `letter` and `shiny`, which Red has no

tests/mod_qol_hooks_tests.lua

@@ -266,13 +266,49 @@ end
 
 do
   local BattleState = require("src.battle.BattleState")
+  local Gen2BattleState = require("src.ui.gen2.BattleState")
   local battle = { wideLayout = function() return false end }
   check(not BattleState.moveGridNavigation(battle),
     "classic move navigation stays a list without a mod")
+  check(not Gen2BattleState.moveGridNavigation({}),
+    "Gold move navigation stays a list without a mod")
   local unsub = wrap("battle.move_grid_navigation", function() return true end)
   check(BattleState.moveGridNavigation(battle),
     "a mod can opt the classic move menu into grid navigation")
+  check(Gen2BattleState.moveGridNavigation({}),
+    "the same hook opts Gold's move menu into grid navigation")
+
+  local pressed, moveCount = "right", 4
+  local gold = setmetatable({
+    phase = "moves", moveIndex = 1,
+    slideFrame = math.huge,
+    game = { input = {
+      wasPressed = function(_, key) return key == pressed end,
+    } },
+    updateAlarm = function() end,
+    stepHpAnim = function() return false end,
+    playerMoves = function()
+      local moves = {}
+      for i = 1, moveCount do moves[i] = {} end
+      return moves
+    end,
+  }, { __index = Gen2BattleState })
+  gold:update(0)
+  check(gold.moveIndex == 2,
+    "Gold grid navigation moves right across a companion move row")
+  pressed, gold.moveIndex = "down", 1
+  gold:update(0)
+  check(gold.moveIndex == 3,
+    "Gold grid navigation moves down the companion move column")
+  pressed, moveCount, gold.moveIndex = "down", 3, 2
+  gold:update(0)
+  check(gold.moveIndex == 2,
+    "Gold grid navigation does not select an empty fourth move slot")
   unsub()
+  pressed, gold.moveIndex = "right", 1
+  gold:update(0)
+  check(gold.moveIndex == 1,
+    "removing the hook restores Gold's native vertical move list")
   battle.wideLayout = function() return true end
   check(BattleState.moveGridNavigation(battle),
     "the native wide move grid remains enabled without a mod")