Add gate to increase post-feed page size (#5473)

* Add gate to increase post-feed page size

* Exclude Discover

* Remove exception

* Clarify intent

* Let gate cache

src/lib/statsig/gates.ts

@@ -1,3 +1,5 @@
 export type Gate =
   // Keep this alphabetic please.
-  'debug_show_feedcontext' | 'suggested_feeds_interstitial'
+  | 'debug_show_feedcontext'
+  | 'post_feed_lang_window'
+  | 'suggested_feeds_interstitial'

src/state/queries/post-feed.ts

@@ -28,6 +28,7 @@ import {FeedTuner, FeedTunerFn} from '#/lib/api/feed-manip'
 import {DISCOVER_FEED_URI} from '#/lib/constants'
 import {BSKY_FEED_OWNER_DIDS} from '#/lib/constants'
 import {moderatePost_wrapped as moderatePost} from '#/lib/moderatePost_wrapped'
+import {useGate} from '#/lib/statsig/statsig'
 import {logger} from '#/logger'
 import {STALE} from '#/state/queries'
 import {DEFAULT_LOGGED_OUT_PREFERENCES} from '#/state/queries/preferences/const'
@@ -109,13 +110,19 @@ export interface FeedPage {
   fetchedAt: number
 }
 
-const PAGE_SIZE = 30
+/**
+ * The minimum number of posts we want in a single "page" of results. Since we
+ * filter out unwanted content, we may fetch more than this number to ensure
+ * that we get _at least_ this number.
+ */
+const MIN_POSTS = 30
 
 export function usePostFeedQuery(
   feedDesc: FeedDescriptor,
   params?: FeedParams,
   opts?: {enabled?: boolean; ignoreFilterFor?: string},
 ) {
+  const gate = useGate()
   const feedTuners = useFeedTuners(feedDesc)
   const moderationOpts = useModerationOpts()
   const {data: preferences} = usePreferencesQuery()
@@ -135,6 +142,13 @@ export function usePostFeedQuery(
   } | null>(null)
   const isDiscover = feedDesc.includes(DISCOVER_FEED_URI)
 
+  /**
+   * The number of posts to fetch in a single request. Because we filter
+   * unwanted content, we may over-fetch here to try and fill pages by
+   * `MIN_POSTS`.
+   */
+  const fetchLimit = gate('post_feed_lang_window') ? 100 : MIN_POSTS
+
   // Make sure this doesn't invalidate unless really needed.
   const selectArgs = React.useMemo(
     () => ({
@@ -175,7 +189,7 @@ export function usePostFeedQuery(
           }
 
       try {
-        const res = await api.fetch({cursor, limit: PAGE_SIZE})
+        const res = await api.fetch({cursor, limit: fetchLimit})
 
         /*
          * If this is a public view, we need to check if posts fail moderation.
@@ -373,13 +387,13 @@ export function usePostFeedQuery(
     // Now track how many items we really want, and fetch more if needed.
     if (isLoading || isRefetching) {
       // During the initial fetch, we want to get an entire page's worth of items.
-      wantedItemCount.current = PAGE_SIZE
+      wantedItemCount.current = MIN_POSTS
     } else if (isFetchingNextPage) {
       if (itemCount > wantedItemCount.current) {
         // We have more items than wantedItemCount, so wantedItemCount must be out of date.
         // Some other code must have called fetchNextPage(), for example, from onEndReached.
         // Adjust the wantedItemCount to reflect that we want one more full page of items.
-        wantedItemCount.current = itemCount + PAGE_SIZE
+        wantedItemCount.current = itemCount + MIN_POSTS
       }
     } else if (hasNextPage) {
       // At this point we're not fetching anymore, so it's time to make a decision.