Fix timeline pagination in the WebUI (#9516)

The `hasMore` property of timelines in redux store was set whenever an API
request returned only one page of results, *even* if the query only requested
newer statuses (using `since_id`), causing `hasMore` to be incorrectly set to
false whenever fetching new toots in a timeline, which happens each time
an account's timeline or media gallery is visited.

app/javascript/mastodon/actions/timelines.js

@@ -74,12 +74,14 @@ export function expandTimeline(timelineId, path, params = {}, done = noOp) {
       params.since_id = timeline.getIn(['items', 0]);
     }
 
+    const isLoadingRecent = !!params.since_id;
+
     dispatch(expandTimelineRequest(timelineId, isLoadingMore));
 
     api(getState).get(path, { params }).then(response => {
       const next = getLinks(response).refs.find(link => link.rel === 'next');
       dispatch(importFetchedStatuses(response.data));
-      dispatch(expandTimelineSuccess(timelineId, response.data, next ? next.uri : null, response.code === 206, isLoadingMore));
+      dispatch(expandTimelineSuccess(timelineId, response.data, next ? next.uri : null, response.code === 206, isLoadingRecent, isLoadingMore));
       done();
     }).catch(error => {
       dispatch(expandTimelineFail(timelineId, error, isLoadingMore));
@@ -112,13 +114,14 @@ export function expandTimelineRequest(timeline, isLoadingMore) {
   };
 };
 
-export function expandTimelineSuccess(timeline, statuses, next, partial, isLoadingMore) {
+export function expandTimelineSuccess(timeline, statuses, next, partial, isLoadingRecent, isLoadingMore) {
   return {
     type: TIMELINE_EXPAND_SUCCESS,
     timeline,
     statuses,
     next,
     partial,
+    isLoadingRecent,
     skipLoading: !isLoadingMore,
   };
 };

app/javascript/mastodon/reducers/timelines.js

@@ -26,10 +26,10 @@ const initialTimeline = ImmutableMap({
   items: ImmutableList(),
 });
 
-const expandNormalizedTimeline = (state, timeline, statuses, next, isPartial) => {
+const expandNormalizedTimeline = (state, timeline, statuses, next, isPartial, isLoadingRecent) => {
   return state.update(timeline, initialTimeline, map => map.withMutations(mMap => {
     mMap.set('isLoading', false);
-    if (!next) mMap.set('hasMore', false);
+    if (!next && !isLoadingRecent) mMap.set('hasMore', false);
 
     if (!statuses.isEmpty()) {
       mMap.update('items', ImmutableList(), oldIds => {
@@ -126,7 +126,7 @@ export default function timelines(state = initialState, action) {
   case TIMELINE_EXPAND_FAIL:
     return state.update(action.timeline, initialTimeline, map => map.set('isLoading', false));
   case TIMELINE_EXPAND_SUCCESS:
-    return expandNormalizedTimeline(state, action.timeline, fromJS(action.statuses), action.next, action.partial);
+    return expandNormalizedTimeline(state, action.timeline, fromJS(action.statuses), action.next, action.partial, action.isLoadingRecent);
   case TIMELINE_UPDATE:
     return updateTimeline(state, action.timeline, fromJS(action.status));
   case TIMELINE_DELETE: