Add a special-case to ScrollPanel list height calculation for when the timeline is very barren

Author: t3chguy

src/components/structures/ScrollPanel.tsx

@@ -28,12 +28,11 @@ const DEBUG_SCROLL = false;
 // The amount of extra scroll distance to allow prior to unfilling.
 // See getExcessHeight.
 const UNPAGINATION_PADDING = 6000;
-// The number of milliseconds to debounce calls to onUnfillRequest, to prevent
-// many scroll events causing many unfilling requests.
+// The number of milliseconds to debounce calls to onUnfillRequest,
+// to prevent many scroll events causing many unfilling requests.
 const UNFILL_REQUEST_DEBOUNCE_MS = 200;
-// _updateHeight makes the height a ceiled multiple of this so we
-// don't have to update the height too often. It also allows the user
-// to scroll past the pagination spinner a bit so they don't feel blocked so
+// updateHeight makes the height a ceiled multiple of this so we don't have to update the height too often.
+// It also allows the user to scroll past the pagination spinner a bit so they don't feel blocked so
 // much while the content loads.
 const PAGE_SIZE = 400;
 
@@ -192,16 +191,14 @@ export default class ScrollPanel extends React.Component<IProps> {
     private preventShrinkingState: IPreventShrinkingState;
     private unfillDebouncer: number;
     private bottomGrowth: number;
-    private pages: number;
+    private minListHeight: number;
     private heightUpdateInProgress: boolean;
     private divScroll: HTMLDivElement;
 
     constructor(props, context) {
         super(props, context);
 
-        if (this.props.resizeNotifier) {
-            this.props.resizeNotifier.on("middlePanelResizedNoisy", this.onResize);
-        }
+        this.props.resizeNotifier?.on("middlePanelResizedNoisy", this.onResize);
 
         this.resetScrollState();
     }
@@ -227,9 +224,7 @@ export default class ScrollPanel extends React.Component<IProps> {
         // (We could use isMounted(), but facebook have deprecated that.)
         this.unmounted = true;
 
-        if (this.props.resizeNotifier) {
-            this.props.resizeNotifier.removeListener("middlePanelResizedNoisy", this.onResize);
-        }
+        this.props.resizeNotifier?.removeListener("middlePanelResizedNoisy", this.onResize);
     }
 
     private onScroll = ev => {
@@ -541,7 +536,7 @@ export default class ScrollPanel extends React.Component<IProps> {
             stuckAtBottom: this.props.startAtBottom,
         };
         this.bottomGrowth = 0;
-        this.pages = 0;
+        this.minListHeight = 0;
         this.scrollTimeout = new Timer(100);
         this.heightUpdateInProgress = false;
     };
@@ -734,9 +729,13 @@ export default class ScrollPanel extends React.Component<IProps> {
         const sn = this.getScrollNode();
         const itemlist = this.itemlist.current;
         const contentHeight = this.getMessagesHeight();
-        const minHeight = sn.clientHeight;
-        const height = Math.max(minHeight, contentHeight);
-        this.pages = Math.ceil(height / PAGE_SIZE);
+        // Only round to the nearest page when we're basing the height off the content, not off the scrollNode height
+        // otherwise it'll cause too much overscroll which makes it possible to entirely scroll content off-screen.
+        if (contentHeight < sn.clientHeight - PAGE_SIZE) {
+            this.minListHeight = sn.clientHeight;
+        } else {
+            this.minListHeight = Math.ceil(contentHeight / PAGE_SIZE) * PAGE_SIZE;
+        }
         this.bottomGrowth = 0;
         const newHeight = `${this.getListHeight()}px`;
 
@@ -805,7 +804,7 @@ export default class ScrollPanel extends React.Component<IProps> {
     }
 
     private getListHeight(): number {
-        return this.bottomGrowth + (this.pages * PAGE_SIZE);
+        return this.bottomGrowth + this.minListHeight;
     }
 
     private getMessagesHeight(): number {