perf(launcher): keep mod index navigation responsive

src/import/LauncherView.lua

@@ -3056,8 +3056,8 @@ local function buildFindKindRow(imp, x, y, w, m)
 end
 
 local function buildFindPanel(imp, x, y, w, availH, m)
+  imp._findVisibleEntries = nil
   imp:_ensureFind()
-  imp:_ensureMods()
   local ModIndex = require("src.mods.ModIndex")
   local ModUpdate = require("src.mods.ModUpdate")
   local sources = imp.findSources or {}
@@ -3126,7 +3126,9 @@ local function buildFindPanel(imp, x, y, w, availH, m)
 
   if #rows == 0 then
     local empty
-    if carts then
+    if imp._findFetch then
+      empty = Strings("Loading mod index...")
+    elseif carts then
       empty = (total == 0) and Strings("This index lists no carts yet.")
         or Strings("No carts match that search.")
     else
@@ -3191,6 +3193,11 @@ local function buildFindPanel(imp, x, y, w, availH, m)
   local listTop = cy
   setPage(imp, "find", Kit.wheelPage(x, listTop, w, listH, cur, #rows, perPage))
 
+  local visible = imp._findVisibleEntries or {}
+  for i = #visible, 1, -1 do visible[i] = nil end
+  for i = first, last do visible[#visible + 1] = rows[i] end
+  imp._findVisibleEntries = visible
+
   for i = first, last do
     local entry = rows[i]
     local ry = listTop + (i - first) * (rowH + gap)
@@ -5764,12 +5771,6 @@ local function loaderSpec(imp)
     return { title = b.title, detail = b.detail, progress = b.progress,
              onCancel = b.cancel }
   end
-  -- The boot prewarm runs without an overlay (the user did not ask for it and
-  -- must be able to use the launcher meanwhile), but if they reach the Find
-  -- Mods tab before it lands, THEN they are waiting on it and it earns one.
-  if imp.tab == "find" and imp._findFetch and not imp.findLoaded then
-    return { title = Strings("Loading mod index") }
-  end
   return nil
 end
 

src/import/RomImporter.lua

@@ -1390,8 +1390,9 @@ function RomImporter.new(onComplete, opts)
     -- player's index list from options; findIndex is the merged listing;
     -- _findThumbs caches one image per mod id (false = fetched and failed).
     findLoaded = false, findSources = nil, findIndex = nil,
-    findScroll = 0, findNotice = nil, findQuery = "", findCategory = nil,
-    _findSearchFocus = false, _findThumbs = nil,
+    findInstalled = nil, findScroll = 0, findNotice = nil, findQuery = "",
+    findCategory = nil, _findSearchFocus = false, _findThumbs = nil,
+    _findVisibleEntries = nil,
     -- Which half of the feed the panel is browsing.  Mods by default: carts
     -- are the newer, much shorter list, and a feed may carry none at all.
     findKind = "mods", findBase = nil,
@@ -2589,6 +2590,7 @@ function RomImporter:update(dt)
   -- before a tab switch still completes.
   self:_pumpFindFetch()
   self:_pumpModInfoFetch()
+  self:_queueFindEnrichment()
   self:_pumpFindStats()
   self:_pumpFindThumbs()
   self:_pumpSkinFetch()
@@ -3226,6 +3228,7 @@ end
 -- offset persists inside the view's per-tab scroll container.
 function RomImporter:_switchTab(id)
   self.tab = id
+  if id ~= "find" then self._findVisibleEntries = nil end
   self._findSearchFocus = false
   self._skinUrlFocus = false
   self:_disarmTextInput()
@@ -3823,6 +3826,7 @@ function RomImporter:_toggleSafeMode()
   SaveData.saveOptions(options)
   self.safeMode = enabled
   self.mods = nil
+  self.findInstalled = nil
   self._modSortCache = nil
   self._modInfoFetch = nil
   self.modNotice = nil
@@ -4798,6 +4802,7 @@ function RomImporter:_refreshMods()
   local LauncherMods = require("src.mods.LauncherMods")
   local SaveData = require("src.core.SaveData")
   self._cartPlan = nil
+  self.findInstalled = nil
   self.safeMode = SaveData.isSafeMode(SaveData.loadOptions())
   -- Once per session, ahead of the first listing: pull in any mod the player
   -- unzipped beside the executable, which an ordinary (non-portable) install
@@ -5718,7 +5723,8 @@ end
 -- as long as the slowest index took -- measured at over two minutes on a
 -- cold open, with no spinner, because the frame that would have drawn one
 -- never ran.  The fetch now starts here and completes across later frames in
--- _pumpFindFetch; the loader overlay is up for the whole flight.
+-- _pumpFindFetch.  Only an explicit Refresh is blocking; boot prewarm and the
+-- first visit keep the launcher interactive while the listing arrives.
 function RomImporter:_refreshFind(force)
   -- The notice is the fix, not the gate (#876).  This branch used to return an
   -- empty listing silently, and because the player had by then added a source,
@@ -5756,10 +5762,12 @@ function RomImporter:_refreshFind(force)
     carts = {}, cartSeen = {}, bases = {}, baseSeen = {},
     stale = false, oldest = nil, at = 1,
   }
+  if force == true then
     self:_setBusy(Strings("Fetching mod index"),
       #sources == 1 and (sources[1].label or sources[1].feed)
         or Strings("%d indexes", #sources))
   end
+end
 
 -- Drive the in-flight index fetch one frame at a time.  Called from update().
 function RomImporter:_pumpFindFetch()
@@ -5958,9 +5966,17 @@ end
 
 function RomImporter:_findInstalledMap()
   if self:findingCarts() then return self:_findInstalledCarts() end
-  local map = {}
-  for _, m in ipairs(self.mods or {}) do map[m.id] = m.version or true end
-  return map
+  if self.findInstalled then return self.findInstalled end
+  local LauncherMods = require("src.mods.LauncherMods")
+  if self.mods then
+    self.findInstalled = {}
+    for _, m in ipairs(self.mods) do
+      self.findInstalled[m.id] = m.version or true
+    end
+  else
+    self.findInstalled = LauncherMods.installedVersions() or {}
+  end
+  return self.findInstalled
 end
 
 -- id -> installed version for every cart on disk, whatever game it plays as.
@@ -5978,10 +5994,9 @@ function RomImporter:_findInstalledCarts()
   return map
 end
 
--- One thumbnail per frame, and only for a card actually on screen: the fetch
--- is a blocking curl, so downloading a whole listing's worth on open would
--- stall the launcher for as many seconds as there are mods.  A failure is
--- remembered as `false` so a broken URL is tried once, not every frame.
+-- Read the cached thumbnail for a card.  Starting a download is deliberately
+-- separate: immediate-mode draw may call this for every visible row, but it
+-- must not mutate the fetch queue or perform network work.
 function RomImporter:_findThumb(entry)
   self._findThumbs = self._findThumbs or {}
   local cached = self._findThumbs[entry.id]
@@ -5992,6 +6007,20 @@ function RomImporter:_findThumb(entry)
     self._findThumbs[entry.id] = false
     return nil
   end
+  return nil
+end
+
+-- Queue one thumbnail after draw has recorded the visible rows.  The fetch
+-- pool runs off-thread; only the finished image decode stays in update().
+function RomImporter:_startFindThumb(entry)
+  self._findThumbs = self._findThumbs or {}
+  if self._findThumbs[entry.id] ~= nil then return end
+  local ModIndex = require("src.mods.ModIndex")
+  local url = ModIndex.joinUrl(entry._base, entry.thumbnail)
+  if not url then
+    self._findThumbs[entry.id] = false
+    return
+  end
   -- ASYNC (was one blocking download per frame).  Only rows on the current
   -- page ever ask, so pagination already bounds this to a page's worth of
   -- requests; the fetch pool runs them off-thread and the card shows its
@@ -6112,9 +6141,9 @@ function RomImporter:_requestFindStats(entry)
   }
 end
 
--- Request-and-read, for a row that is being drawn and for the detail modal.
+-- Read-only accessor for a row being drawn or shown in the detail modal.
+-- Network work is scheduled by _queueFindEnrichment from update().
 function RomImporter:_findStats(entry)
-  self:_requestFindStats(entry)
   return self:_findStatsCached(entry)
 end
 
@@ -6134,6 +6163,38 @@ function RomImporter:_findThumbPending(id)
   return (self._findThumbFetch and self._findThumbFetch[id]) ~= nil
 end
 
+-- Draw records the visible page in _findVisibleEntries.  Queue only a small
+-- batch from that snapshot during update(), keeping network scheduling out of
+-- the immediate-mode render path and preventing a large index from creating a
+-- burst of thumbnail/GitHub work in one frame.
+local FIND_ENRICH_PER_FRAME = 2
+
+function RomImporter:_queueFindEnrichment()
+  if self.tab ~= "find" or not self.findLoaded then return end
+  local visible = self._findVisibleEntries
+  if not visible then return end
+  local thumbnails, stats = 0, 0
+  for _, entry in ipairs(visible) do
+    if thumbnails < FIND_ENRICH_PER_FRAME
+        and self:_findThumb(entry) == nil
+        and not self:_findThumbPending(entry.id) then
+      self:_startFindThumb(entry)
+      thumbnails = thumbnails + 1
+    end
+    if stats < FIND_ENRICH_PER_FRAME
+        and self:_findStatsCached(entry) == nil
+        and entry.github and entry.github ~= ""
+        and not self:_findStatsPendingFor(entry.id) then
+      self:_requestFindStats(entry)
+      stats = stats + 1
+    end
+    if thumbnails >= FIND_ENRICH_PER_FRAME
+        and stats >= FIND_ENRICH_PER_FRAME then
+      break
+    end
+  end
+end
+
 -- Drive in-flight FIND MODS stats lookups.  Called from update().
 function RomImporter:_pumpFindStats()
   local pending = self._findStatsPending

src/mods/LauncherMods.lua

@@ -471,6 +471,20 @@ discover = function()
   return out
 end
 
+-- installedVersions() -> id -> installed version.  MOD INDEX only needs to
+-- know whether a listing is already present; it does not need enablement,
+-- dependency/conflict status, required-import validation, or migration.  Keep
+-- that cheap read separate from list(), whose richer work belongs to MODS.
+function LauncherMods.installedVersions()
+  local out = {}
+  local ok, manifests = pcall(discover)
+  if not ok then return out end
+  for _, manifest in ipairs(manifests or {}) do
+    out[manifest.id] = manifest.version or true
+  end
+  return out
+end
+
 -- list([version]) -> the mods-panel rows for the current install.  Reads the
 -- same enable-state the loader persists, so a toggle here is what the game
 -- sees on its next boot; `version` narrows that to one game's answers.

tests/engine/launcher_mod_downloads.lua

@@ -75,7 +75,8 @@ end
 do
   local ri = launcher()
   check(ri:_findStats(entry("nulled", nil, "someone/nulled")) == nil,
-        "a null count is not an answer; the repo is still consulted")
+        "a null count is not an answer")
+  ri:_requestFindStats(entry("nulled", nil, "someone/nulled"))
   eq(#fetched, 1, "which is the fetch the panel already made for dates")
 
   local bare = launcher()
@@ -83,7 +84,7 @@ do
   check(stats ~= nil and stats.total == nil,
         "a listing with neither counts nor a repo is resolved-but-unknown")
   check(stats.recent == nil, "and has nothing to trend on")
-  eq(#fetched, 1, "and queues nothing of its own")
+  eq(#fetched, 1, "and the explicit scheduler queues nothing without a repo")
 end
 
 -- A real zero is not unknown: the index has seen the releases and counted

tests/engine/launcher_navigation_perf.lua

@@ -0,0 +1,88 @@
+-- Launcher navigation performance seams.  MOD INDEX must not pay the full
+-- MODS validation pass, background index prefetch must not create a blocking
+-- overlay, and visible-row enrichment must be scheduled from update state
+-- rather than from immediate-mode draw calls.
+--   luajit tests/engine/launcher_navigation_perf.lua
+
+package.path = "./?.lua;./?/init.lua;" .. package.path
+if not _G.love then _G.love = require("tests.love_stub") end
+
+local T = require("tests.harness")
+local check, eq = T.check, T.eq
+local LauncherMods = require("src.mods.LauncherMods")
+local ModIndex = require("src.mods.ModIndex")
+local RomImporter = require("src.import.RomImporter")
+
+check(type(LauncherMods.installedVersions) == "function",
+  "LauncherMods exposes a lightweight installed-version scan")
+
+do
+  local old = LauncherMods.installedVersions
+  local called = 0
+  LauncherMods.installedVersions = function()
+    called = called + 1
+    return { alpha = "1.2.3" }
+  end
+  local imp = setmetatable({}, RomImporter)
+  local installed = imp:_findInstalledMap()
+  eq(called, 1, "MOD INDEX asks for the lightweight scan when MODS is cold")
+  eq(installed.alpha, "1.2.3",
+    "the lightweight scan supplies installed versions")
+  LauncherMods.installedVersions = old
+end
+
+do
+  local imp = setmetatable({ tab = "find", findLoaded = false }, RomImporter)
+  imp._refreshFindSources = function(self)
+    self.findSources = { { feed = "https://example.invalid/index.json" } }
+  end
+  local oldBegin = ModIndex.beginFetch
+  ModIndex.beginFetch = function() return { test = true } end
+  imp:_refreshFind(false)
+  check(imp._findFetch ~= nil, "background index refresh starts asynchronously")
+  eq(imp._busy, nil,
+    "background index refresh does not block navigation with a loader")
+  imp:_clearBusy()
+  imp._findFetch = nil
+  ModIndex.beginFetch = oldBegin
+end
+
+do
+  local requests = 0
+  local imp = setmetatable({ tab = "find", findLoaded = true,
+    _findVisibleEntries = {
+      { id = "one", thumbnail = "one.png", github = "a/one" },
+      { id = "two", thumbnail = "two.png", github = "a/two" },
+      { id = "three", thumbnail = "three.png", github = "a/three" },
+    } }, RomImporter)
+  imp._findThumb = function() return nil end
+  imp._findThumbPending = function() return false end
+  imp._findStatsCached = function() return nil end
+  imp._startFindThumb = function() requests = requests + 1 end
+  imp._requestFindStats = function() requests = requests + 1 end
+  imp:_queueFindEnrichment()
+  eq(requests, 4,
+    "update schedules a bounded thumbnail and stats batch for visible rows")
+end
+
+do
+  local requests = 0
+  local imp = setmetatable({}, RomImporter)
+  imp._findStatsCached = function() return nil end
+  imp._requestFindStats = function() requests = requests + 1 end
+  imp:_findStats({ id = "draw-only", github = "a/draw-only" })
+  eq(requests, 0, "reading row stats during draw never starts a request")
+end
+
+do
+  local f = assert(io.open("src/import/LauncherView.lua", "rb"))
+  local src = f:read("*a")
+  f:close()
+  local start = assert(src:find("local function buildFindPanel", 1, true))
+  local finish = assert(src:find("\nlocal function ", start + 1, true))
+  local panel = src:sub(start, finish - 1)
+  check(not panel:find("imp:_ensureMods()", 1, true),
+    "MOD INDEX panel does not force the full MODS list")
+end
+
+T.finish("launcher_navigation_perf")