refactor(chat): replace timeline scroll engine with anchored-turn LegendList

Sending a message now parks that message near the top of the viewport
and streams the reply into reserved end space below it, instead of
jumping to the bottom and chasing it.

- swap @tanstack/react-virtual for @legendapp/list in the chat timeline; the
  streaming tail becomes a normal list row rather than a separately rendered
  block, so one component owns the scroll position
- add timelineScrollAnchoring: pure anchored-turn geometry plus the three
  scroll modes (following-end / anchoring-new-turn / free-scrolling)
- replace useChatAutoFollow with useChatTimelineScroll, which opts out of
  automatic movement on real gestures via a generation counter instead of the
  timer windows the old implementation needed to recognise its own writes
- move the load-older button, question/permission cards, recap, status row and
  bottom spacer into the list header/footer, since the list owns its container
- extract useScrollShadow so the shadows can attach to that container

maintainScrollAtEnd and maintainVisibleContentPosition replace the manual
prepend anchor-hold and the mobile quiet-window prepend deferral.

Validated: workspace type-check, lint, web build, ui tests per file.
Scroll behaviour itself is unverified and needs manual testing on web, desktop
and iOS.
This commit is contained in:
Bohdan Triapitsyn
2026-08-25 01:10:00 +03:00
parent 3b7d5e1c34
commit d2d8669564
18 changed files with 1739 additions and 1536 deletions
+149 -82
View File
@@ -18,8 +18,8 @@ import { StatusRowContainer } from './StatusRowContainer';
import { SessionRecapNote } from '@/components/chat/SessionRecapSpacer';
import ScrollToBottomButton from './components/ScrollToBottomButton';
import { PromptNavigatorRail } from './components/PromptNavigatorRail';
import { ScrollShadow } from '@/components/ui/ScrollShadow';
import { useChatAutoFollow, type AnimationHandlers, type ContentChangeReason } from '@/hooks/useChatAutoFollow';
import { useScrollShadow } from '@/components/ui/useScrollShadow';
import { useChatTimelineScroll, type AnimationHandlers, type ContentChangeReason, type TimelineListHandle } from '@/hooks/useChatTimelineScroll';
import { useChatTimelineController } from './hooks/useChatTimelineController';
import { TimelineDialog } from './TimelineDialog';
import { useChatTurnNavigation } from './hooks/useChatTurnNavigation';
@@ -151,10 +151,16 @@ type ChatViewportProps = {
currentSessionKey: string;
isDesktopExpandedInput: boolean;
isMobile: boolean;
stickyUserHeader: boolean;
directory?: string;
scrollRef: React.RefObject<HTMLDivElement | null>;
messageListRef: React.RefObject<MessageListHandle | null>;
registerList: (list: TimelineListHandle | null) => void;
anchorMessageId: string | null;
onAnchorReady: (messageId: string, anchorIndex: number) => void;
onAnchorSizeChanged: (messageId: string) => void;
composerOverlayHeight: number;
onIsAtEndChange: (isAtEnd: boolean) => void;
onTimelineDataChange: () => void;
pendingRevealWork: boolean;
renderedMessages: SessionMessageRecord[];
isLoadingOlder: boolean;
@@ -169,7 +175,6 @@ type ChatViewportProps = {
} | null;
handleMessageContentChange: (reason?: ContentChangeReason) => void;
getAnimationHandlers: (messageId: string) => AnimationHandlers;
handleHistoryScroll: () => void;
scrollToBottom: () => void;
sessionQuestions: QuestionRequest[];
sessionPermissions: PermissionRequest[];
@@ -190,10 +195,16 @@ const ChatViewport = React.memo(({
currentSessionKey,
isDesktopExpandedInput,
isMobile,
stickyUserHeader,
directory,
scrollRef,
messageListRef,
registerList,
anchorMessageId,
onAnchorReady,
onAnchorSizeChanged,
composerOverlayHeight,
onIsAtEndChange,
onTimelineDataChange,
pendingRevealWork,
renderedMessages,
isLoadingOlder,
@@ -203,7 +214,6 @@ const ChatViewport = React.memo(({
retryOverlay,
handleMessageContentChange,
getAnimationHandlers,
handleHistoryScroll,
scrollToBottom,
sessionQuestions,
sessionPermissions,
@@ -315,6 +325,60 @@ const ChatViewport = React.memo(({
scrollRef.current?.focus({ preventScroll: true });
}, [scrollRef]);
// Everything that used to sit beside the list inside the scroll container
// now renders as the list's header/footer, so it keeps scrolling with the
// rows exactly as before.
const listHeader = React.useMemo(() => (
showLoadOlderButton ? (
<div className="flex justify-center pt-3 pb-1">
<Button
variant="secondary"
size="sm"
onClick={onLoadOlder}
disabled={isLoadingOlder}
>
{isLoadingOlder && (
<Icon name="loader-4" className="size-4 animate-spin" />
)}
{t('chat.history.loadOlder')}
</Button>
</div>
) : null
), [isLoadingOlder, onLoadOlder, showLoadOlderButton, t]);
const listFooter = React.useMemo(() => (
<>
{(sessionQuestions.length > 0 || sessionPermissions.length > 0) && (
<div>
{sessionQuestions.map((question) => (
<QuestionCard key={question.id} question={question} />
))}
{sessionPermissions.map((permission) => (
<PermissionCard key={permission.id} permission={permission} />
))}
</div>
)}
<SessionRecapNote sessionId={currentSessionId} directory={directory} isMobile={isMobile} />
<div className="mb-3">
<StatusRowContainer />
</div>
<div className="flex-shrink-0" style={{ height: isMobile ? '40px' : '10vh' }} aria-hidden="true" />
</>
), [currentSessionId, directory, isMobile, sessionPermissions, sessionQuestions]);
const scrollContainerProps = React.useMemo(() => ({
className: 'absolute inset-0 overflow-y-auto overflow-x-hidden z-0 chat-scroll overlay-scrollbar-target',
style: CHAT_SCROLL_STYLE,
tabIndex: 0,
onClick: focusScrollContainer,
'data-scrollbar': 'chat',
'data-scroll-shadow': 'true',
'data-orientation': 'vertical',
}), [focusScrollContainer]);
return (
<div
className={cn(
@@ -326,71 +390,32 @@ const ChatViewport = React.memo(({
aria-hidden={isDesktopExpandedInput}
>
<div className="absolute inset-0">
<ScrollShadow
className="absolute inset-0 overflow-y-auto overflow-x-hidden z-0 chat-scroll overlay-scrollbar-target"
ref={scrollRef}
style={CHAT_SCROLL_STYLE}
observeMutations={false}
hideTopShadow={isMobile && stickyUserHeader}
tabIndex={0}
onClick={focusScrollContainer}
onScroll={handleHistoryScroll}
data-scroll-shadow="true"
data-scrollbar="chat"
>
<div className="relative z-0 min-h-full">
{showLoadOlderButton && (
<div className="flex justify-center pt-3 pb-1">
<Button
variant="secondary"
size="sm"
onClick={onLoadOlder}
disabled={isLoadingOlder}
>
{isLoadingOlder && (
<Icon name="loader-4" className="size-4 animate-spin" />
)}
{t('chat.history.loadOlder')}
</Button>
</div>
)}
<MessageList
key={currentSessionKey}
ref={messageListRef}
sessionKey={currentSessionId}
disableStaging={pendingRevealWork}
messages={renderedMessages}
sessionIsWorking={sessionIsWorking}
activeStreamingMessageId={streamingMessageId}
activeStreamingPhase={activeStreamingPhase}
retryOverlay={retryOverlay}
onMessageContentChange={handleMessageContentChange}
getAnimationHandlers={getAnimationHandlers}
isLoadingOlder={isLoadingOlder}
scrollToBottom={scrollToBottom}
scrollRef={scrollRef}
directory={directory}
/>
{(sessionQuestions.length > 0 || sessionPermissions.length > 0) && (
<div>
{sessionQuestions.map((question) => (
<QuestionCard key={question.id} question={question} />
))}
{sessionPermissions.map((permission) => (
<PermissionCard key={permission.id} permission={permission} />
))}
</div>
)}
<SessionRecapNote sessionId={currentSessionId} directory={directory} isMobile={isMobile} />
<div className="mb-3">
<StatusRowContainer />
</div>
<div className="flex-shrink-0" style={{ height: isMobile ? '40px' : '10vh' }} aria-hidden="true" />
</div>
</ScrollShadow>
<MessageList
key={currentSessionKey}
ref={messageListRef}
sessionKey={currentSessionId}
disableStaging={pendingRevealWork}
messages={renderedMessages}
sessionIsWorking={sessionIsWorking}
activeStreamingMessageId={streamingMessageId}
activeStreamingPhase={activeStreamingPhase}
retryOverlay={retryOverlay}
onMessageContentChange={handleMessageContentChange}
getAnimationHandlers={getAnimationHandlers}
isLoadingOlder={isLoadingOlder}
scrollToBottom={scrollToBottom}
directory={directory}
registerList={registerList}
anchorMessageId={anchorMessageId}
onAnchorReady={onAnchorReady}
onAnchorSizeChanged={onAnchorSizeChanged}
composerOverlayHeight={composerOverlayHeight}
onIsAtEndChange={onIsAtEndChange}
onTimelineDataChange={onTimelineDataChange}
listHeader={listHeader}
listFooter={listFooter}
scrollContainerProps={scrollContainerProps}
/>
<OverlayScrollbar containerRef={scrollRef} suppressVisibility={isProgrammaticFollowActive} userIntentOnly observeMutations={false} />
{showPromptNavigator && promptTurnIds.length >= 2 ? (
<PromptNavigatorRail
@@ -411,7 +436,6 @@ const ChatViewport = React.memo(({
&& prev.currentSessionKey === next.currentSessionKey
&& prev.isDesktopExpandedInput === next.isDesktopExpandedInput
&& prev.isMobile === next.isMobile
&& prev.stickyUserHeader === next.stickyUserHeader
&& prev.directory === next.directory
&& prev.scrollRef === next.scrollRef
&& prev.messageListRef === next.messageListRef
@@ -424,7 +448,6 @@ const ChatViewport = React.memo(({
&& prev.retryOverlay === next.retryOverlay
&& prev.handleMessageContentChange === next.handleMessageContentChange
&& prev.getAnimationHandlers === next.getAnimationHandlers
&& prev.handleHistoryScroll === next.handleHistoryScroll
&& prev.scrollToBottom === next.scrollToBottom
&& prev.sessionQuestions === next.sessionQuestions
&& prev.sessionPermissions === next.sessionPermissions
@@ -891,23 +914,44 @@ export const ChatContainer: React.FC<ChatContainerProps> = ({
activeTurnChangeRef.current(turnId);
}, []);
// The composer sits below the timeline rather than over it, so no part of
// the scroll container is occluded. Mobile surfaces that float the composer
// pass their measured height here instead.
const composerOverlayHeight = 0;
const lastUserMessageId = React.useMemo(() => {
for (let index = sessionMessages.length - 1; index >= 0; index -= 1) {
const message = sessionMessages[index];
if (message.info.role === 'user') {
return message.info.id;
}
}
return null;
}, [sessionMessages]);
const {
scrollRef,
scrollNode,
registerList,
anchorMessageId,
onAnchorReady,
onAnchorSizeChanged,
onIsAtEndChange,
onManualNavigation,
onTimelineDataChange,
notifyContentChange: handleMessageContentChange,
getAnimationHandlers,
goToBottom,
scrollToBottomOnSend,
releaseAutoFollow,
restoreSnapshot,
isPinned,
isFollowingProgrammatically,
showScrollButton,
} = useChatAutoFollow({
} = useChatTimelineScroll({
currentSessionId,
currentSessionKey,
sessionMessageCount,
sessionIsWorking,
isMobile,
composerOverlayHeight,
lastUserMessageId,
onActiveTurnChange: handleActiveTurnChange,
});
@@ -922,10 +966,28 @@ export const ChatContainer: React.FC<ChatContainerProps> = ({
messageListRef,
loadMoreMessages,
goToBottom,
releaseAutoFollow,
releaseAutoFollow: onManualNavigation,
isPinned,
showScrollButton,
});
// The list owns the scroll element, so the shadows and the load-older
// trigger bind to its node rather than to a wrapper we render.
const scrollNodeRef = React.useMemo(() => ({ current: scrollNode }), [scrollNode]);
useScrollShadow(scrollNodeRef, {
observeMutations: false,
hideTopShadow: isMobile && stickyUserHeader,
});
const handleHistoryScroll = timelineController.handleHistoryScroll;
React.useEffect(() => {
if (!scrollNode) return;
const onScroll = () => handleHistoryScroll();
scrollNode.addEventListener('scroll', onScroll, { passive: true });
return () => {
scrollNode.removeEventListener('scroll', onScroll);
};
}, [handleHistoryScroll, scrollNode]);
const resumeToLatestInstant = React.useCallback(() => {
goToBottom('instant');
}, [goToBottom]);
@@ -1084,7 +1146,7 @@ export const ChatContainer: React.FC<ChatContainerProps> = ({
lastScrolledSessionKeyRef.current = currentSessionKey;
if (hasHashTarget) {
// Hash navigation handler will scroll to target; we just release auto-follow.
releaseAutoFollow();
onManualNavigation();
return;
}
@@ -1096,7 +1158,7 @@ export const ChatContainer: React.FC<ChatContainerProps> = ({
} else {
window.requestAnimationFrame(run);
}
}, [active, currentSessionId, currentSessionKey, releaseAutoFollow, restoreSnapshot]);
}, [active, currentSessionId, currentSessionKey, onManualNavigation, restoreSnapshot]);
React.useEffect(() => {
if (!messagesEnabled || !currentSessionId) return;
@@ -1265,9 +1327,15 @@ export const ChatContainer: React.FC<ChatContainerProps> = ({
currentSessionKey={currentSessionKey ?? currentSessionId ?? ''}
isDesktopExpandedInput={isDesktopExpandedInput}
isMobile={isMobile}
stickyUserHeader={stickyUserHeader}
directory={effectiveSessionDirectory}
scrollRef={scrollRef}
registerList={registerList}
anchorMessageId={anchorMessageId}
onAnchorReady={onAnchorReady}
onAnchorSizeChanged={onAnchorSizeChanged}
composerOverlayHeight={composerOverlayHeight}
onIsAtEndChange={onIsAtEndChange}
onTimelineDataChange={onTimelineDataChange}
messageListRef={messageListRef}
pendingRevealWork={timelineController.pendingRevealWork}
renderedMessages={timelineController.renderedMessages}
@@ -1278,7 +1346,6 @@ export const ChatContainer: React.FC<ChatContainerProps> = ({
retryOverlay={retryOverlay}
handleMessageContentChange={handleMessageContentChange}
getAnimationHandlers={getAnimationHandlers}
handleHistoryScroll={timelineController.handleHistoryScroll}
scrollToBottom={resumeToLatestInstant}
sessionQuestions={sessionQuestions}
sessionPermissions={sessionPermissions}
@@ -14,7 +14,7 @@ import { useThemeSystem } from '@/contexts/useThemeSystem';
import { cn } from '@/lib/utils';
import { useChatSurfaceMode } from './useChatSurfaceMode';
import type { AnimationHandlers, ContentChangeReason } from '@/hooks/useChatAutoFollow';
import type { AnimationHandlers, ContentChangeReason } from '@/hooks/useChatTimelineScroll';
import MessageBody from './message/MessageBody';
import type { AgentMentionInfo } from './message/types';
import type { StreamPhase, ToolPopupContent } from './message/types';
+343 -407
View File
@@ -1,11 +1,11 @@
import React from 'react';
import type { Part } from '@opencode-ai/sdk/v2';
import { elementScroll, useVirtualizer as useTanstackVirtualizer, type ReactVirtualizer, type VirtualItem } from '@tanstack/react-virtual';
import { LegendList, type LegendListRef } from '@legendapp/list/react';
import ChatMessage from './ChatMessage';
import { areOptionalRenderRelevantMessagesEqual, areRelevantTurnGroupingContextsEqual, areRenderRelevantMessagesEqual } from './message/renderCompare';
import TurnItem from './components/TurnItem';
import type { AnimationHandlers, ContentChangeReason } from '@/hooks/useChatAutoFollow';
import type { AnimationHandlers, ContentChangeReason } from '@/hooks/useChatTimelineScroll';
import type { ChatMessageEntry, TurnRecord, TurnGroupingContext } from './lib/turns/types';
import { useTurnRecords } from './hooks/useTurnRecords';
import { applyRetryOverlay } from './lib/turns/applyRetryOverlay';
@@ -20,8 +20,8 @@ import { streamPerfCount, streamPerfMark, streamPerfMeasure } from '@/stores/uti
import type { StreamPhase } from './message/types';
import { useGlobalSessionsStore } from '@/stores/useGlobalSessionsStore';
import { useSessionParts } from '@/sync/sync-context';
import { isMobileSurfaceRuntime } from '@/lib/runtimeSurface';
import type { ReviewTransferDirection } from '@/lib/reviewFlow';
import { resolveChatListAnchoredEndSpace, resolveTimelineIsAtEnd } from './lib/scroll/timelineScrollAnchoring';
import {
USER_SHELL_MARKER,
isUserShellMarkerMessage,
@@ -29,96 +29,52 @@ import {
type ShellBridgeDetails,
} from './lib/shellBridge';
const MESSAGE_LIST_VIRTUALIZE_THRESHOLD = 5;
const EMPTY_STATIC_ENTRY_MESSAGES: ChatMessageEntry[] = [];
const EMPTY_UNGROUPED_MESSAGE_IDS = new Set<string>();
const TIMELINE_CACHE_LIMIT = 16;
const sameKeys = (a: readonly string[] | undefined, b: readonly string[] | undefined): boolean => {
if (a === b) return true;
if (!a || !b) return false;
if (a.length !== b.length) return false;
return a.every((key, index) => key === b[index]);
};
// --- Timeline virtualization (@legendapp/list) -----------------------------
// The timeline is a single virtualized list on every surface: history turns
// AND the live streaming tail are rows of the same list, so the list owns one
// coherent scroll position instead of arbitrating between a virtualizer and a
// separately-rendered tail.
//
// Scroll behavior the list owns natively, which is why none of it exists here
// any more:
// • `maintainScrollAtEnd` keeps the live edge pinned as rows grow.
// • `maintainVisibleContentPosition` preserves the read position when older
// history is prepended, replacing the manual anchor-hold and the mobile
// quiet-window prepend deferral.
// • `anchoredEndSpace` reserves the tail space that parks a just-sent
// message near the top of the viewport.
const TIMELINE_ESTIMATED_ENTRY_SIZE = 320;
// --- History virtualization (@tanstack/react-virtual) ----------------------
// The history list virtualizes with @tanstack/react-virtual on all surfaces:
// its core has bottom anchoring (anchorTo: 'end'), key-stable prepend
// preservation, and native iOS touch/momentum deferral for scroll
// adjustments — the failure modes that historically forced virtua off on
// mobile and required manual prepend compensation on desktop.
type TanstackVirtualizerInstance = ReactVirtualizer<HTMLDivElement, HTMLDivElement>;
type HistoryEngine = 'none' | 'tanstack';
const TANSTACK_ESTIMATED_ENTRY_SIZE = 320;
const TANSTACK_OVERSCAN = 8;
// Touch flings cover more distance between paints than desktop wheels; a
// larger window keeps fast mobile scrolling over mounted rows.
const TANSTACK_MOBILE_OVERSCAN = 16;
const resolveTanstackOverscan = (): number => (
isMobileSurfaceRuntime() ? TANSTACK_MOBILE_OVERSCAN : TANSTACK_OVERSCAN
);
// Post-prepend anchor hold: measurements of freshly
// prepended rows settle over multiple frames, so a single restore can be
// invalidated by the next measurement pass. Re-assert the anchor until it
// holds still for STABLE_FRAMES consecutive frames, giving up at MAX_FRAMES.
// Anchor hold for an explicit viewport restore (session re-entry): row
// measurements settle over several frames, so a single restore can be
// invalidated by the next measurement pass. Re-assert until it holds still for
// STABLE_FRAMES consecutive frames, giving up at MAX_FRAMES.
const ANCHOR_HOLD_STABLE_FRAMES = 30;
const ANCHOR_HOLD_MAX_FRAMES = 180;
// Adaptive estimate bounds: only trust the session average once a few rows
// are measured, and keep it inside sane turn-height bounds.
const TANSTACK_ESTIMATE_MIN_SAMPLES = 5;
const TANSTACK_ESTIMATE_MIN = 120;
const TANSTACK_ESTIMATE_MAX = 1200;
// "At bottom" tolerance for resize-adjustment decisions.
const TANSTACK_AT_END_THRESHOLD_PX = 80;
// Quiet-window prepend on mobile: while a touch drag or momentum scroll is
// active, iOS owns the scroll position and ANY geometry change above the
// viewport races against the native animation — a race that compensation
// logic can only lose sometimes. So freshly loaded older history is held
// (data already fetched, store already updated) and inserted into the
// rendered list only once the gesture goes quiet. Safety valves: flush when
// the user gets close to the top (a blank top is worse than a small hop) or
// after MAX_HOLD_MS.
const HISTORY_PREPEND_QUIET_MS = 160;
const HISTORY_PREPEND_MAX_HOLD_MS = 1500;
const HISTORY_PREPEND_NEAR_TOP_VIEWPORTS = 1.5;
const HISTORY_PREPEND_MONITOR_INTERVAL_MS = 90;
// A commit is a deferable prepend when older entries were inserted strictly
// above the known content: the previous first key still exists deeper in the
// list and the tail is unchanged. Anything else renders immediately.
const isPrependAboveCommit = (previous: RenderEntry[], next: RenderEntry[]): boolean => {
if (previous.length === 0 || next.length <= previous.length) return false;
if (previous[previous.length - 1]?.key !== next[next.length - 1]?.key) return false;
const previousFirstKey = previous[0]?.key;
const insertedIndex = next.findIndex((entry) => entry.key === previousFirstKey);
return insertedIndex > 0;
// Reserved tail space that parks an anchored row near the top of the viewport.
// `onReady` fires once the list has measured the anchor, `onSizeChanged` when
// the reserved size is recomputed.
// Presentation-only props forwarded to the scroll container the list renders.
// Deliberately narrow: the list owns scroll and layout callbacks on that
// element, so only styling, focus and click-through are caller-controlled.
type TimelineScrollContainerProps = {
className?: string;
style?: React.CSSProperties;
tabIndex?: number;
onClick?: React.MouseEventHandler<HTMLDivElement>;
'data-scrollbar'?: string;
'data-scroll-shadow'?: string;
};
const tanstackTimelineCache = new Map<string, { keys: readonly string[]; items: VirtualItem[] }>();
const readTanstackTimelineCache = (sessionKey: string, keys: readonly string[]): VirtualItem[] | undefined => {
const entry = tanstackTimelineCache.get(sessionKey);
if (!entry) return undefined;
if (sameKeys(entry.keys, keys)) return entry.items;
tanstackTimelineCache.delete(sessionKey);
return undefined;
};
const writeTanstackTimelineCache = (
sessionKey: string,
keys: readonly string[],
virtualizer: TanstackVirtualizerInstance | null | undefined,
): void => {
if (!virtualizer || keys.length === 0) return;
tanstackTimelineCache.delete(sessionKey);
tanstackTimelineCache.set(sessionKey, { keys: keys.slice(), items: virtualizer.takeSnapshot() });
while (tanstackTimelineCache.size > TIMELINE_CACHE_LIMIT) {
const oldest = tanstackTimelineCache.keys().next().value;
if (typeof oldest !== 'string') break;
tanstackTimelineCache.delete(oldest);
}
type TimelineAnchoredEndSpace = {
anchorIndex: number;
anchorOffset?: number;
onReady?: (info: { anchorIndex: number | undefined; anchorKey: string | undefined; size: number }) => void;
onSizeChanged?: (size: number) => void;
};
const useStableEvent = <TArgs extends unknown[], TResult>(handler: (...args: TArgs) => TResult) => {
@@ -365,8 +321,24 @@ interface MessageListProps {
getAnimationHandlers: (messageId: string) => AnimationHandlers;
isLoadingOlder: boolean;
scrollToBottom?: () => void;
scrollRef?: React.RefObject<HTMLDivElement | null>;
directory?: string;
// The list owns its scroll container; the timeline scroll hook drives it
// through this ref and observes it through the callbacks below.
registerList?: (list: LegendListRef | null) => void;
// The anchored row is identified by message id; the index it maps to is a
// property of the row model, which only this component knows.
anchorMessageId?: string | null;
onAnchorReady?: (messageId: string, anchorIndex: number) => void;
onAnchorSizeChanged?: (messageId: string) => void;
composerOverlayHeight?: number;
onIsAtEndChange?: (isAtEnd: boolean) => void;
onTimelineDataChange?: () => void;
// Content that used to sit as siblings of the list inside the scroll
// container. The list owns that container now, so they render as its
// header/footer and scroll with the rows exactly as before.
listHeader?: React.ReactNode;
listFooter?: React.ReactNode;
scrollContainerProps?: TimelineScrollContainerProps;
}
export interface MessageListHandle {
@@ -929,14 +901,10 @@ const MessageListEntry = React.memo(({
MessageListEntry.displayName = 'MessageListEntry';
// Inner component that renders staged turn entries.
type StaticHistoryListProps = {
entries: RenderEntry[];
engine: HistoryEngine;
contentRef: React.RefObject<HTMLDivElement | null>;
scrollRef?: React.RefObject<HTMLDivElement | null>;
registerTanstackVirtualizer?: (virtualizer: TanstackVirtualizerInstance | null) => void;
virtualizerKey: string;
// Shared row state. Passed through context rather than closed over by
// `renderItem` so the render callback keeps a stable identity — a changing
// `renderItem` makes the list re-render every mounted row on every commit.
type TimelineRowContextValue = {
onMessageContentChange: (reason?: ContentChangeReason) => void;
getAnimationHandlers: (messageId: string) => AnimationHandlers;
scrollToBottom?: () => void;
@@ -945,242 +913,176 @@ type StaticHistoryListProps = {
turnUiStates: Map<string, TurnUiState>;
onToggleTurnGroup: (turnId: string) => void;
chatRenderMode: 'sorted' | 'live';
showTurnChangedFiles: boolean;
shouldAnimateUserMessage: (message: ChatMessageEntry) => boolean;
onUserAnimationConsumed: (messageId: string) => void;
reviewTransferDirection?: ReviewTransferDirection | null;
// The live tail row renders through StreamingTailContent, which subscribes
// to streaming parts; every other row renders statically.
streamingTailKey: string | null;
directory?: string;
sessionIsWorking: boolean;
activeStreamingMessageId: string | null;
activeStreamingPhase: StreamPhase | null;
};
const StaticHistoryList = React.memo(({ entries, engine, contentRef, scrollRef, registerTanstackVirtualizer, virtualizerKey, onMessageContentChange, getAnimationHandlers, scrollToBottom, stickyUserHeader, defaultActivityExpanded, turnUiStates, onToggleTurnGroup, chatRenderMode, shouldAnimateUserMessage, onUserAnimationConsumed, reviewTransferDirection }: StaticHistoryListProps) => {
const isTanstack = engine === 'tanstack';
const TimelineRowContext = React.createContext<TimelineRowContextValue | null>(null);
// --- Quiet-window prepend (mobile) --------------------------------------
// Gesture tracking for the deferred-prepend decision. Refs only: reading
// them never re-renders, and the render-phase reconcile below needs them.
const touchActiveRef = React.useRef(false);
const lastScrollAtRef = React.useRef(0);
const holdSinceRef = React.useRef<number | null>(null);
const deferPrepends = isTanstack && isMobileSurfaceRuntime();
const TimelineRow = React.memo(({ entry }: { entry: RenderEntry }) => {
const context = React.useContext(TimelineRowContext);
if (!context) return null;
React.useEffect(() => {
if (!deferPrepends) return;
const element = scrollRef?.current;
if (!element) return;
const onTouchStart = () => { touchActiveRef.current = true; };
const onTouchEnd = () => { touchActiveRef.current = false; };
const onScroll = () => { lastScrollAtRef.current = performance.now(); };
element.addEventListener('touchstart', onTouchStart, { passive: true });
element.addEventListener('touchend', onTouchEnd, { passive: true });
element.addEventListener('touchcancel', onTouchEnd, { passive: true });
element.addEventListener('scroll', onScroll, { passive: true });
return () => {
element.removeEventListener('touchstart', onTouchStart);
element.removeEventListener('touchend', onTouchEnd);
element.removeEventListener('touchcancel', onTouchEnd);
element.removeEventListener('scroll', onScroll);
};
}, [deferPrepends, scrollRef]);
const isGestureActive = React.useCallback(() => (
touchActiveRef.current
|| performance.now() - lastScrollAtRef.current < HISTORY_PREPEND_QUIET_MS
), []);
const isNearTop = React.useCallback(() => {
const element = scrollRef?.current;
if (!element) return true;
return element.scrollTop < element.clientHeight * HISTORY_PREPEND_NEAR_TOP_VIEWPORTS;
}, [scrollRef]);
const [displayEntries, setDisplayEntries] = React.useState(entries);
// Render-phase reconcile (official derived-state pattern): adopt the new
// entries immediately unless this commit is a pure prepend-above landing
// in the middle of an active touch gesture — those wait for quiet.
let renderEntries = displayEntries;
if (entries !== displayEntries) {
const shouldHold = deferPrepends
&& isPrependAboveCommit(displayEntries, entries)
&& isGestureActive()
&& !isNearTop()
&& (holdSinceRef.current === null
|| performance.now() - holdSinceRef.current < HISTORY_PREPEND_MAX_HOLD_MS);
if (shouldHold) {
if (holdSinceRef.current === null) holdSinceRef.current = performance.now();
} else {
holdSinceRef.current = null;
setDisplayEntries(entries);
renderEntries = entries;
}
} else if (holdSinceRef.current !== null) {
holdSinceRef.current = null;
}
// While a prepend is held, poll for the quiet window (touch/momentum have
// no completion event we can await) and flush by re-rendering.
const [, forceFlushTick] = React.useReducer((tick: number) => tick + 1, 0);
React.useEffect(() => {
if (!deferPrepends) return;
const timer = window.setInterval(() => {
if (holdSinceRef.current === null) return;
const expired = performance.now() - holdSinceRef.current >= HISTORY_PREPEND_MAX_HOLD_MS;
if (!isGestureActive() || isNearTop() || expired) {
forceFlushTick();
}
}, HISTORY_PREPEND_MONITOR_INTERVAL_MS);
return () => window.clearInterval(timer);
}, [deferPrepends, isGestureActive, isNearTop]);
const entriesRef = React.useRef(renderEntries);
entriesRef.current = renderEntries;
// Initial-only read: measurement cache restore is a mount-time concern;
// afterwards the live virtualizer owns measurements.
const [initialMeasurements] = React.useState(() => (
isTanstack
? readTanstackTimelineCache(virtualizerKey, entries.map((entry) => entry.key))
: undefined
));
const sizeContainerRef = React.useRef<HTMLDivElement | null>(null);
// Adaptive estimate: rows this session has actually measured are a far
// better predictor for the still-unmeasured ones than a fixed constant.
// Smaller estimate error → smaller anchor corrections when prepended rows
// measure in → less visible drift. The ref keeps estimateSize's identity
// stable so updating the average never triggers a global remeasure.
const estimatedEntrySizeRef = React.useRef(TANSTACK_ESTIMATED_ENTRY_SIZE);
const tanstackVirtualizer = useTanstackVirtualizer<HTMLDivElement, HTMLDivElement>({
count: renderEntries.length,
enabled: isTanstack,
getScrollElement: () => scrollRef?.current ?? null,
estimateSize: () => estimatedEntrySizeRef.current,
overscan: resolveTanstackOverscan(),
scrollToFn: (offset, options, instance) => {
// Expose the new total height before core writes an anchor
// correction so the browser does not clamp the offset to the old
// height.
const sizeElement = sizeContainerRef.current;
if (sizeElement) sizeElement.style.height = `${instance.getTotalSize()}px`;
elementScroll(offset, options, instance);
},
getItemKey: (index) => entriesRef.current[index]?.key ?? `index:${index}`,
// Bottom-anchored chat semantics: prepending older entries above the
// viewport must not move what the user is reading, and iOS-specific
// touch/momentum deferral for those adjustments lives in the core.
anchorTo: 'end',
initialOffset: () => Number.MAX_SAFE_INTEGER,
initialMeasurementsCache: initialMeasurements,
});
// Only compensate scroll for rows growing ABOVE the viewport (history
// remeasures, prepended pages). A row growing inside the viewport —
// expanding a tool call or thinking block — must grow DOWNWARD naturally;
// the end-anchored default made it expand upward. At the bottom,
// app-level auto-follow owns pinning, so skip there too instead of
// double-writing. (This is an instance field, not a constructor option.)
tanstackVirtualizer.shouldAdjustScrollPositionOnItemSizeChange = (item, _delta, instance) => {
if (instance.isAtEnd(TANSTACK_AT_END_THRESHOLD_PX)) return false;
const firstVisibleIndex = instance.range?.startIndex;
return firstVisibleIndex !== undefined && item.index < firstVisibleIndex;
};
React.useEffect(() => {
if (!isTanstack) return;
const sizes = tanstackVirtualizer.itemSizeCache;
if (sizes.size >= TANSTACK_ESTIMATE_MIN_SAMPLES) {
let total = 0;
for (const size of sizes.values()) total += size;
estimatedEntrySizeRef.current = Math.min(
TANSTACK_ESTIMATE_MAX,
Math.max(TANSTACK_ESTIMATE_MIN, Math.round(total / sizes.size)),
);
}
});
React.useEffect(() => {
if (!isTanstack) return;
registerTanstackVirtualizer?.(tanstackVirtualizer);
return () => {
writeTanstackTimelineCache(
virtualizerKey,
entriesRef.current.map((entry) => entry.key),
tanstackVirtualizer,
);
registerTanstackVirtualizer?.(null);
};
}, [isTanstack, registerTanstackVirtualizer, tanstackVirtualizer, virtualizerKey]);
const renderEntry = React.useCallback((entry: RenderEntry) => {
if (context.streamingTailKey === entry.key) {
return (
<MessageListEntry
key={entry.key}
<StreamingTailContent
entry={entry}
onMessageContentChange={onMessageContentChange}
getAnimationHandlers={getAnimationHandlers}
scrollToBottom={scrollToBottom}
stickyUserHeader={stickyUserHeader}
sessionIsWorking={false}
defaultActivityExpanded={defaultActivityExpanded}
turnUiStates={turnUiStates}
onToggleTurnGroup={onToggleTurnGroup}
chatRenderMode={chatRenderMode}
shouldAnimateUserMessage={shouldAnimateUserMessage}
onUserAnimationConsumed={onUserAnimationConsumed}
activeStreamingMessageId={null}
activeStreamingPhase={null}
reviewTransferDirection={reviewTransferDirection}
directory={context.directory}
onMessageContentChange={context.onMessageContentChange}
getAnimationHandlers={context.getAnimationHandlers}
scrollToBottom={context.scrollToBottom}
stickyUserHeader={context.stickyUserHeader}
sessionIsWorking={context.sessionIsWorking}
defaultActivityExpanded={context.defaultActivityExpanded}
turnUiStates={context.turnUiStates}
onToggleTurnGroup={context.onToggleTurnGroup}
chatRenderMode={context.chatRenderMode}
showTurnChangedFiles={context.showTurnChangedFiles}
shouldAnimateUserMessage={context.shouldAnimateUserMessage}
onUserAnimationConsumed={context.onUserAnimationConsumed}
activeStreamingMessageId={context.activeStreamingMessageId}
activeStreamingPhase={context.activeStreamingPhase}
reviewTransferDirection={context.reviewTransferDirection}
/>
);
}, [chatRenderMode, defaultActivityExpanded, getAnimationHandlers, onMessageContentChange, onToggleTurnGroup, onUserAnimationConsumed, reviewTransferDirection, scrollToBottom, shouldAnimateUserMessage, stickyUserHeader, turnUiStates]);
if (engine === 'none') {
return (
<div ref={contentRef} className="relative w-full">
{renderEntries.map((entry) => (
<div
key={entry.key}
data-turn-entry={entry.key}
>
{renderEntry(entry)}
</div>
))}
</div>
);
}
if (engine === 'tanstack') {
const virtualItems = tanstackVirtualizer.getVirtualItems();
const startOffset = virtualItems[0]?.start ?? 0;
// Rendered rows stay in normal flow inside a single offset wrapper (not
// per-row absolute positioning) so per-turn sticky user headers keep
// working against the scroll container. The offset MUST be padding, not
// transform: a transformed ancestor becomes the sticky containing block,
// so headers would stick to the wrapper's (arbitrary, overscan-dependent)
// top edge mid-list and float over the previous turn. Padding only
// changes when the virtual window shifts — not per scroll frame — so the
// layout cost is negligible.
return (
<div ref={sizeContainerRef} className="relative w-full" style={{ height: tanstackVirtualizer.getTotalSize() }}>
<div style={{ paddingTop: `${startOffset}px` }}>
{virtualItems.map((item) => {
const entry = renderEntries[item.index];
if (!entry) return null;
return (
<div
key={entry.key}
data-index={item.index}
ref={tanstackVirtualizer.measureElement}
data-turn-entry={entry.key}
>
{renderEntry(entry)}
</div>
);
})}
</div>
</div>
);
}
return null;
return (
<MessageListEntry
entry={entry}
onMessageContentChange={context.onMessageContentChange}
getAnimationHandlers={context.getAnimationHandlers}
scrollToBottom={context.scrollToBottom}
stickyUserHeader={context.stickyUserHeader}
sessionIsWorking={false}
defaultActivityExpanded={context.defaultActivityExpanded}
turnUiStates={context.turnUiStates}
onToggleTurnGroup={context.onToggleTurnGroup}
chatRenderMode={context.chatRenderMode}
shouldAnimateUserMessage={context.shouldAnimateUserMessage}
onUserAnimationConsumed={context.onUserAnimationConsumed}
activeStreamingMessageId={null}
activeStreamingPhase={null}
reviewTransferDirection={context.reviewTransferDirection}
/>
);
});
StaticHistoryList.displayName = 'StaticHistoryList';
TimelineRow.displayName = 'TimelineRow';
const timelineKeyExtractor = (item: RenderEntry): string => item.key;
// Row type drives container reuse. Turn blocks and ungrouped messages have very
// different shapes, so keeping them in separate pools avoids re-measuring a
// container every time one replaces the other.
const timelineItemType = (item: RenderEntry): string => item.kind;
const renderTimelineItem = ({ item }: { item: RenderEntry }) => <TimelineRow entry={item} />;
type TimelineListProps = {
entries: RenderEntry[];
streamingTailKey: string | null;
registerList: (list: LegendListRef | null) => void;
anchoredEndSpace?: {
anchorIndex: number;
anchorOffset?: number;
onReady?: (info: { anchorIndex: number | undefined; anchorKey: string | undefined; size: number }) => void;
onSizeChanged?: (size: number) => void;
};
composerOverlayHeight: number;
onIsAtEndChange: (isAtEnd: boolean) => void;
onTimelineDataChange: () => void;
listHeader?: React.ReactNode;
listFooter?: React.ReactNode;
scrollContainerProps?: TimelineScrollContainerProps;
rowContext: TimelineRowContextValue;
};
const TimelineList = React.memo(({
entries,
registerList,
anchoredEndSpace,
composerOverlayHeight,
onIsAtEndChange,
onTimelineDataChange,
listHeader,
listFooter,
scrollContainerProps,
rowContext,
}: TimelineListProps) => {
const listRef = React.useRef<LegendListRef | null>(null);
const isAtEndRef = React.useRef(true);
const setListRef = React.useCallback((list: LegendListRef | null) => {
listRef.current = list;
registerList(list);
}, [registerList]);
// The list reports scroll continuously; only end-crossings are interesting,
// so the edge is debounced to a state transition here rather than pushing a
// callback on every frame.
const handleScroll = React.useCallback(() => {
const state = listRef.current?.getState();
if (!state) return;
const isAtEnd = resolveTimelineIsAtEnd(state);
if (typeof isAtEnd !== 'boolean' || isAtEnd === isAtEndRef.current) return;
isAtEndRef.current = isAtEnd;
onIsAtEndChange(isAtEnd);
}, [onIsAtEndChange]);
// Data changes are the only moment an automatic correction can be needed;
// the owning hook decides whether one actually applies.
React.useEffect(() => {
onTimelineDataChange();
}, [entries, onTimelineDataChange]);
const header = React.useMemo(() => (listHeader ? <>{listHeader}</> : undefined), [listHeader]);
const footer = React.useMemo(() => (listFooter ? <>{listFooter}</> : undefined), [listFooter]);
return (
<TimelineRowContext.Provider value={rowContext}>
<LegendList<RenderEntry>
ref={setListRef}
data={entries}
keyExtractor={timelineKeyExtractor}
getItemType={timelineItemType}
renderItem={renderTimelineItem}
estimatedItemSize={TIMELINE_ESTIMATED_ENTRY_SIZE}
initialScrollAtEnd
// Chat rows own internal state (expanded tool calls, reveal
// animations); recycling a container into a different row would
// carry that state across.
recycleItems={false}
{...(anchoredEndSpace ? { anchoredEndSpace } : {})}
contentInsetEndAdjustment={composerOverlayHeight}
// While a turn is anchored, the reserved end space — not the
// live edge — defines where the viewport rests.
maintainScrollAtEnd={anchoredEndSpace
? false
: { animated: false, on: { dataChange: true, itemLayout: true, layout: true } }}
// Prepending older history must not move what the user is
// reading. Size restoration stays off: rows growing in place
// (a tool result expanding) must grow downward.
maintainVisibleContentPosition={{ data: true, size: false }}
onScroll={handleScroll}
ListHeaderComponent={header}
ListFooterComponent={footer}
{...scrollContainerProps}
/>
</TimelineRowContext.Provider>
);
});
TimelineList.displayName = 'TimelineList';
const StreamingTailContent: React.FC<{
entry: RenderEntry;
@@ -1262,8 +1164,17 @@ const MessageList = React.forwardRef<MessageListHandle, MessageListProps>(({
onMessageContentChange,
getAnimationHandlers,
scrollToBottom,
scrollRef,
directory,
registerList,
anchorMessageId = null,
onAnchorReady,
onAnchorSizeChanged,
composerOverlayHeight = 0,
onIsAtEndChange,
onTimelineDataChange,
listHeader,
listFooter,
scrollContainerProps,
}, ref) => {
streamPerfMark('react.message_list_render');
streamPerfCount('ui.message_list.render');
@@ -1357,16 +1268,18 @@ const MessageList = React.forwardRef<MessageListHandle, MessageListProps>(({
return output;
}), [messages]);
const historyContentRef = React.useRef<HTMLDivElement | null>(null);
const resolveScrollContainer = React.useCallback((): HTMLDivElement | null => {
if (scrollRef?.current) {
return scrollRef.current;
// The list owns the scroll container. The DOM fallback covers the window
// between mount and the list handing us its node.
const resolveScrollContainer = React.useCallback((): HTMLElement | null => {
const listNode = listRef.current?.getScrollableNode();
if (listNode) {
return listNode;
}
if (typeof document === 'undefined') {
return null;
}
return document.querySelector<HTMLDivElement>('[data-scrollbar="chat"]');
}, [scrollRef]);
}, []);
const displayMessages = React.useMemo(() => streamPerfMeasure('ui.message_list.retry_overlay_ms', () => {
return applyRetryOverlay(baseDisplayMessages, {
@@ -1483,19 +1396,14 @@ const MessageList = React.forwardRef<MessageListHandle, MessageListProps>(({
return { ...entry, nextEntryFirstMessage };
});
}, [staticRenderEntries, trailingEntryFirstMessage]);
// Mobile always starts with the same virtualized engine it will use after
// pagination. Switching a short list from normal DOM to TanStack during a
// prepend remounts the history subtree, and the newly enabled end-anchored
// virtualizer initializes at the bottom before it has prior keyed state.
// Desktop keeps the small-list threshold where that transition is not tied
// to the explicit mobile load-older interaction.
const shouldVirtualizeHistory = isMobileSurfaceRuntime()
|| historyEntries.length >= MESSAGE_LIST_VIRTUALIZE_THRESHOLD;
const historyEngine: HistoryEngine = shouldVirtualizeHistory ? 'tanstack' : 'none';
const tanstackVirtualizerRef = React.useRef<TanstackVirtualizerInstance | null>(null);
const registerTanstackVirtualizer = React.useCallback((virtualizer: TanstackVirtualizerInstance | null) => {
tanstackVirtualizerRef.current = virtualizer;
}, []);
// Every surface uses the same virtualized list for the whole timeline —
// there is no small-list DOM path to transition out of, which is what used
// to remount the history subtree mid-prepend.
const listRef = React.useRef<LegendListRef | null>(null);
const handleRegisterList = React.useCallback((list: LegendListRef | null) => {
listRef.current = list;
registerList?.(list);
}, [registerList]);
const allEntries = React.useMemo(() => {
return trailingStreamingEntry ? [...historyEntries, trailingStreamingEntry] : historyEntries;
@@ -1505,8 +1413,14 @@ const MessageList = React.forwardRef<MessageListHandle, MessageListProps>(({
onMessageContentChange(reason);
});
const stableTailContentChange = useStableEvent((reason?: ContentChangeReason) => {
onMessageContentChange(reason);
// Stable identities: these reach the list, where a changing callback would
// re-render every mounted row.
const stableIsAtEndChange = useStableEvent((isAtEnd: boolean) => {
onIsAtEndChange?.(isAtEnd);
});
const stableTimelineDataChange = useStableEvent(() => {
onTimelineDataChange?.();
});
const currentUserOrder = React.useMemo(() => {
@@ -1596,22 +1510,18 @@ const MessageList = React.forwardRef<MessageListHandle, MessageListProps>(({
return false;
}
if (!shouldVirtualizeHistory) {
const list = listRef.current;
if (!list) {
return false;
}
const virtualizer = tanstackVirtualizerRef.current;
if (!virtualizer) {
return false;
}
// Smooth scrolling can stop at a stale offset while unmounted,
// variable-height rows replace estimates with real measurements. Use
// exact auto-reconciliation; mounted targets still take the smooth DOM
// path below.
virtualizer.scrollToIndex(index, { align: 'start', behavior: 'auto' });
// Unanimated: an unmounted target's position is still an estimate, and
// a smooth scroll would end at that stale offset once the real
// measurement replaces it. Mounted targets still take the smooth DOM
// path in scrollMessageElementIntoView.
void list.scrollToIndex({ index, animated: false, viewPosition: 0 });
return true;
}, [historyEntries.length, shouldVirtualizeHistory]);
}, [historyEntries.length]);
const scrollMessageElementIntoView = React.useCallback((messageId: string, behavior: ScrollBehavior = 'auto') => {
const container = resolveScrollContainer();
@@ -1718,7 +1628,9 @@ const MessageList = React.forwardRef<MessageListHandle, MessageListProps>(({
window.requestAnimationFrame(step);
},
isHistoryVirtualized: () => shouldVirtualizeHistory,
// The timeline is always virtualized now; the flag stays so callers
// that branch on it keep compiling and take the virtualized path.
isHistoryVirtualized: () => true,
captureViewportAnchor: () => {
const container = resolveScrollContainer();
@@ -1790,14 +1702,15 @@ const MessageList = React.forwardRef<MessageListHandle, MessageListProps>(({
},
scrollToBottom: () => {
if (shouldVirtualizeHistory && historyEntries.length > 0 && tanstackVirtualizerRef.current) {
tanstackVirtualizerRef.current.scrollToEnd();
const list = listRef.current;
if (list) {
void list.scrollToEnd({ animated: false });
return;
}
const container = resolveScrollContainer();
if (!container) return;
// Overshoot so the browser clamps to the exact fractional
// maximum (scrollHeight is integer-rounded) — see useChatAutoFollow.
// maximum (scrollHeight is integer-rounded).
container.scrollTop = container.scrollHeight + 4096;
},
};
@@ -1814,65 +1727,88 @@ const MessageList = React.forwardRef<MessageListHandle, MessageListProps>(({
return () => {
objectRef.current = null;
};
}, [findMessageElement, historyEntries.length, messageIndexMap, resolveScrollContainer, scrollHistoryIndexIntoView, scrollMessageElementIntoView, shouldVirtualizeHistory, trailingStreamingEntry, turnIndexMap, ref]);
}, [findMessageElement, historyEntries.length, messageIndexMap, resolveScrollContainer, scrollHistoryIndexIntoView, scrollMessageElementIntoView, trailingStreamingEntry, turnIndexMap, ref]);
const disableFadeIn = false;
const anchoredEndSpace = React.useMemo<TimelineAnchoredEndSpace | undefined>(() => {
const resolved = resolveChatListAnchoredEndSpace(
allEntries,
anchorMessageId,
(entry) => (entry.kind === 'turn' ? entry.turn.userMessage.info.id : entry.message.info.id),
);
if (!resolved || !anchorMessageId) {
return undefined;
}
return {
...resolved,
onReady: (info) => {
if (info.anchorIndex === undefined) return;
onAnchorReady?.(anchorMessageId, info.anchorIndex);
},
onSizeChanged: () => {
onAnchorSizeChanged?.(anchorMessageId);
},
};
}, [allEntries, anchorMessageId, onAnchorReady, onAnchorSizeChanged]);
const rowContext = React.useMemo(() => ({
onMessageContentChange: stableHistoryContentChange,
getAnimationHandlers: stableGetAnimationHandlers,
scrollToBottom: stableScrollToBottom,
stickyUserHeader,
defaultActivityExpanded,
turnUiStates,
onToggleTurnGroup: toggleTurnGroup,
chatRenderMode,
showTurnChangedFiles,
shouldAnimateUserMessage,
onUserAnimationConsumed,
reviewTransferDirection,
streamingTailKey: trailingStreamingEntry?.key ?? null,
directory,
sessionIsWorking,
activeStreamingMessageId,
activeStreamingPhase,
}), [
activeStreamingMessageId,
activeStreamingPhase,
chatRenderMode,
defaultActivityExpanded,
directory,
onUserAnimationConsumed,
reviewTransferDirection,
sessionIsWorking,
shouldAnimateUserMessage,
showTurnChangedFiles,
stableGetAnimationHandlers,
stableHistoryContentChange,
stableScrollToBottom,
stickyUserHeader,
toggleTurnGroup,
trailingStreamingEntry?.key,
turnUiStates,
]);
return (
<div>
<FadeInDisabledProvider disabled={disableFadeIn}>
<div className="relative w-full">
{/* Virtualized history rows unmount/remount during scroll;
re-running the reveal fade on every remount reads as
blinking. History content is never "new", so fade-in
is disabled there — the streaming tail keeps it. */}
<FadeInDisabledProvider disabled={shouldVirtualizeHistory}>
<StaticHistoryList
key={sessionKey}
entries={historyEntries}
engine={historyEngine}
contentRef={historyContentRef}
scrollRef={scrollRef}
registerTanstackVirtualizer={registerTanstackVirtualizer}
virtualizerKey={sessionKey}
onMessageContentChange={stableHistoryContentChange}
getAnimationHandlers={stableGetAnimationHandlers}
scrollToBottom={stableScrollToBottom}
stickyUserHeader={stickyUserHeader}
defaultActivityExpanded={defaultActivityExpanded}
turnUiStates={turnUiStates}
onToggleTurnGroup={toggleTurnGroup}
chatRenderMode={chatRenderMode}
shouldAnimateUserMessage={shouldAnimateUserMessage}
onUserAnimationConsumed={onUserAnimationConsumed}
reviewTransferDirection={reviewTransferDirection}
/>
</FadeInDisabledProvider>
{trailingStreamingEntry ? (
<StreamingTailContent
entry={trailingStreamingEntry}
directory={directory}
onMessageContentChange={stableTailContentChange}
getAnimationHandlers={stableGetAnimationHandlers}
scrollToBottom={stableScrollToBottom}
stickyUserHeader={stickyUserHeader}
sessionIsWorking={sessionIsWorking}
defaultActivityExpanded={defaultActivityExpanded}
turnUiStates={turnUiStates}
onToggleTurnGroup={toggleTurnGroup}
chatRenderMode={chatRenderMode}
showTurnChangedFiles={showTurnChangedFiles}
shouldAnimateUserMessage={shouldAnimateUserMessage}
onUserAnimationConsumed={onUserAnimationConsumed}
activeStreamingMessageId={activeStreamingMessageId}
activeStreamingPhase={activeStreamingPhase}
reviewTransferDirection={reviewTransferDirection}
/>
) : null}
</div>
</FadeInDisabledProvider>
</div>
// Virtualized rows unmount/remount during scroll; re-running the reveal
// fade on every remount reads as blinking. Rows are never "new" from the
// list's point of view, so fade-in is disabled for them — content
// arriving inside the streaming tail keeps its own animations.
<FadeInDisabledProvider disabled>
<TimelineList
key={sessionKey}
entries={allEntries}
streamingTailKey={trailingStreamingEntry?.key ?? null}
registerList={handleRegisterList}
anchoredEndSpace={anchoredEndSpace}
composerOverlayHeight={composerOverlayHeight}
onIsAtEndChange={stableIsAtEndChange}
onTimelineDataChange={stableTimelineDataChange}
listHeader={listHeader}
listFooter={listFooter}
scrollContainerProps={scrollContainerProps}
rowContext={rowContext}
/>
</FadeInDisabledProvider>
);
});
@@ -4,7 +4,7 @@ import ProgressiveGroup from '../message/parts/ProgressiveGroup';
import type { TurnActivityRecord } from '../lib/turns/types';
import type { ToolPopupContent } from '../message/types';
import type { StreamPhase } from '../message/types';
import type { ContentChangeReason } from '@/hooks/useChatAutoFollow';
import type { ContentChangeReason } from '@/hooks/useChatTimelineScroll';
interface DiffStats {
additions: number;
@@ -0,0 +1,225 @@
import { describe, expect, test } from 'bun:test';
import {
CHAT_LIST_ANCHOR_OFFSET,
getAnchoredTurnMetrics,
getRowBottom,
resolveChatListAnchoredEndSpace,
resolveTimelineIsAtEnd,
type TimelineListMeasurementState,
} from './timelineScrollAnchoring';
const buildState = ({
positions,
sizes,
scroll = 0,
scrollLength = 700,
}: {
readonly positions: readonly number[];
readonly sizes: readonly number[];
readonly scroll?: number;
readonly scrollLength?: number;
}): TimelineListMeasurementState => ({
data: positions.map((_, index) => index),
scroll,
scrollLength,
positionAtIndex: (index) => positions[index],
sizeAtIndex: (index) => sizes[index],
});
describe('getRowBottom', () => {
test('measures row bottoms from list row position and size', () => {
const state = buildState({ positions: [0, 120], sizes: [80, 40] });
expect(getRowBottom(state, 1)).toBe(160);
});
test('returns null for unmeasured rows', () => {
const state = buildState({ positions: [0], sizes: [80] });
expect(getRowBottom(state, 5)).toBeNull();
});
test('treats a zero-height row as one pixel tall', () => {
const state = buildState({ positions: [0, 120], sizes: [120, 0] });
expect(getRowBottom(state, 1)).toBe(121);
});
});
describe('getAnchoredTurnMetrics', () => {
test('returns null for an empty timeline', () => {
const state = buildState({ positions: [], sizes: [] });
expect(getAnchoredTurnMetrics({
state,
anchorIndex: 0,
composerOverlayHeight: 180,
anchorOffset: CHAT_LIST_ANCHOR_OFFSET,
})).toBeNull();
});
test('treats the active turn as fitting when it fits above the composer', () => {
const state = buildState({
positions: [0, 300, 460],
sizes: [240, 80, 140],
scrollLength: 760,
});
const metrics = getAnchoredTurnMetrics({
state,
anchorIndex: 1,
composerOverlayHeight: 180,
anchorOffset: 16,
});
expect(metrics?.turnHeight).toBe(300);
expect(metrics?.usableViewportHeight).toBe(564);
expect(metrics?.overflowsUsableViewport).toBe(false);
expect(metrics?.targetScrollToRevealEnd).toBe(36);
expect(metrics?.scrollDeltaToRevealEnd).toBe(36);
});
test('targets the real row end instead of any temporary reserved tail', () => {
const state = buildState({
positions: [0, 1720, 1880],
sizes: [1600, 80, 120],
scroll: 1900,
scrollLength: 760,
});
const metrics = getAnchoredTurnMetrics({
state,
anchorIndex: 1,
composerOverlayHeight: 180,
anchorOffset: 16,
});
expect(metrics?.lastBottom).toBe(2000);
expect(metrics?.targetScrollToRevealEnd).toBe(1436);
expect(metrics?.scrollDeltaToRevealEnd).toBe(0);
});
test('reports overflow only for the current anchored turn', () => {
const state = buildState({
positions: [0, 900, 1180],
sizes: [800, 220, 300],
scroll: 900,
scrollLength: 760,
});
const metrics = getAnchoredTurnMetrics({
state,
anchorIndex: 1,
composerOverlayHeight: 180,
anchorOffset: 16,
});
expect(metrics?.turnHeight).toBe(580);
expect(metrics?.usableViewportHeight).toBe(564);
expect(metrics?.overflowsUsableViewport).toBe(true);
});
test('returns the minimal positive scroll delta needed to reveal the turn end', () => {
const state = buildState({
positions: [0, 900, 1180],
sizes: [800, 220, 360],
scroll: 900,
scrollLength: 760,
});
const metrics = getAnchoredTurnMetrics({
state,
anchorIndex: 1,
composerOverlayHeight: 180,
anchorOffset: 16,
});
expect(metrics?.lastBottom).toBe(1540);
expect(metrics?.visibleUsableBottom).toBe(1464);
expect(metrics?.scrollDeltaToRevealEnd).toBe(76);
});
test('subtracts composer height from usable viewport height', () => {
const state = buildState({
positions: [0, 300],
sizes: [120, 470],
scrollLength: 700,
});
const withoutComposer = getAnchoredTurnMetrics({
state,
anchorIndex: 1,
composerOverlayHeight: 0,
anchorOffset: 16,
});
const withComposer = getAnchoredTurnMetrics({
state,
anchorIndex: 1,
composerOverlayHeight: 220,
anchorOffset: 16,
});
expect(withoutComposer?.overflowsUsableViewport).toBe(false);
expect(withComposer?.overflowsUsableViewport).toBe(true);
});
test('clamps an out-of-range anchor index to the last row', () => {
const state = buildState({
positions: [0, 300],
sizes: [240, 80],
scrollLength: 760,
});
const metrics = getAnchoredTurnMetrics({
state,
anchorIndex: 99,
composerOverlayHeight: 0,
anchorOffset: 16,
});
expect(metrics?.anchorTop).toBe(300);
expect(metrics?.turnHeight).toBe(80);
});
});
describe('resolveTimelineIsAtEnd', () => {
test('prefers the near-end threshold over the exact content bottom', () => {
expect(resolveTimelineIsAtEnd({ isNearEnd: true, isAtEnd: false })).toBe(true);
expect(resolveTimelineIsAtEnd({ isNearEnd: false, isAtEnd: true })).toBe(false);
});
test('falls back to the exact end when near-end is unavailable', () => {
expect(resolveTimelineIsAtEnd({ isAtEnd: true })).toBe(true);
});
test('reports nothing without a state', () => {
expect(resolveTimelineIsAtEnd(undefined)).toBe(undefined);
});
});
describe('resolveChatListAnchoredEndSpace', () => {
const rows = [{ id: 'a' }, { id: 'b' }, { id: 'a' }];
test('returns nothing when no anchor is set', () => {
expect(resolveChatListAnchoredEndSpace(rows, null, (row) => row.id)).toBe(undefined);
});
test('returns nothing when the anchor is not in the list', () => {
expect(resolveChatListAnchoredEndSpace(rows, 'z', (row) => row.id)).toBe(undefined);
});
test('resolves the last occurrence so a resent message anchors to its live row', () => {
expect(resolveChatListAnchoredEndSpace(rows, 'a', (row) => row.id)).toEqual({
anchorIndex: 2,
anchorOffset: CHAT_LIST_ANCHOR_OFFSET,
});
});
test('honours an explicit anchor offset', () => {
expect(resolveChatListAnchoredEndSpace(rows, 'b', (row) => row.id, { anchorOffset: 40 })).toEqual({
anchorIndex: 1,
anchorOffset: 40,
});
});
});
@@ -0,0 +1,147 @@
// Anchored-turn scroll geometry for the chat timeline.
//
// The timeline has three mutually exclusive scroll modes:
//
// • `following-end` — stay pinned to the live edge as content grows.
// • `anchoring-new-turn` — the just-sent user message is parked near the TOP
// of the viewport and the reply streams into reserved space below it. The
// viewport does NOT move until the turn outgrows the usable viewport.
// • `free-scrolling` — the user took over; nothing moves the scroll
// position until they opt back in.
//
// This module is pure geometry: it reads measurements from the virtualized
// list and answers "how far, if at all, must we scroll to reveal the end of
// the anchored turn". Keeping it free of DOM and React makes the mode machine
// testable without a renderer.
//
// "Usable viewport" is the visible height minus the composer overlay (the
// composer floats over the list) minus the anchor offset, so a turn is only
// considered overflowing when it genuinely cannot be read.
export type TimelineScrollMode = 'following-end' | 'anchoring-new-turn' | 'free-scrolling';
// Distance from the top of the viewport at which an anchored user message
// parks. Small enough to read as "at the top", large enough not to collide
// with the timeline's top fade.
export const CHAT_LIST_ANCHOR_OFFSET = 16;
export interface TimelineListMeasurementState {
readonly data: readonly unknown[];
readonly scroll: number;
readonly scrollLength: number;
readonly positionAtIndex: (index: number) => number | undefined;
readonly sizeAtIndex: (index: number) => number | undefined;
}
export interface AnchoredTurnMetrics {
readonly anchorTop: number;
readonly lastBottom: number;
readonly turnHeight: number;
readonly usableViewportHeight: number;
readonly visibleUsableBottom: number;
readonly overflowsUsableViewport: boolean;
readonly targetScrollToRevealEnd: number;
readonly scrollDeltaToRevealEnd: number;
}
export const getRowBottom = (
state: TimelineListMeasurementState,
index: number,
): number | null => {
const top = state.positionAtIndex(index);
const height = state.sizeAtIndex(index);
if (
typeof top !== 'number'
|| typeof height !== 'number'
|| !Number.isFinite(top)
|| !Number.isFinite(height)
) {
return null;
}
// Rows measured at zero height would make an anchored turn look empty and
// suppress the reveal scroll; treat them as one pixel tall instead.
return top + Math.max(1, height);
};
export const getAnchoredTurnMetrics = ({
state,
anchorIndex,
composerOverlayHeight,
anchorOffset,
}: {
readonly state: TimelineListMeasurementState;
readonly anchorIndex: number;
readonly composerOverlayHeight: number;
readonly anchorOffset: number;
}): AnchoredTurnMetrics | null => {
if (state.data.length === 0) return null;
const boundedAnchorIndex = Math.max(0, Math.min(anchorIndex, state.data.length - 1));
const anchorTop = state.positionAtIndex(boundedAnchorIndex);
// The LAST row bottom, not the content length: the reserved anchored end
// space lives past it, and targeting that reserved tail would scroll the
// real content off the top.
const lastBottom = getRowBottom(state, state.data.length - 1);
if (typeof anchorTop !== 'number' || !Number.isFinite(anchorTop) || lastBottom === null) {
return null;
}
const usableViewportHeight = Math.max(
0,
state.scrollLength - composerOverlayHeight - anchorOffset,
);
const turnHeight = Math.max(0, lastBottom - anchorTop);
const visibleUsableBottom = state.scroll + usableViewportHeight;
const targetScrollToRevealEnd = Math.max(0, lastBottom - usableViewportHeight);
// Never negative: revealing the end must not scroll the timeline backwards.
const scrollDeltaToRevealEnd = Math.max(0, targetScrollToRevealEnd - state.scroll);
return {
anchorTop,
lastBottom,
turnHeight,
usableViewportHeight,
visibleUsableBottom,
overflowsUsableViewport: turnHeight > usableViewportHeight,
targetScrollToRevealEnd,
scrollDeltaToRevealEnd,
};
};
// "At the end" for follow purposes is the NEAR-end threshold, not the exact
// content bottom: the timeline's footer (status row plus bottom spacer) sits
// below the last row, so requiring the exact bottom would drop out of follow —
// and pop the scroll-to-bottom pill — while the user is still looking at the
// live edge. `isAtEnd` is only the fallback for states that predate the
// near-end signal.
export const resolveTimelineIsAtEnd = (
state: { readonly isNearEnd?: boolean; readonly isAtEnd?: boolean } | undefined,
): boolean | undefined => state?.isNearEnd ?? state?.isAtEnd;
export interface ChatListAnchoredEndSpace {
readonly anchorIndex: number;
readonly anchorOffset: number;
}
// Finds the anchored row from the BACK of the list: a retried or re-sent
// message id can appear more than once, and the live one is always the last.
export const resolveChatListAnchoredEndSpace = <Item, AnchorId>(
items: readonly Item[],
anchorId: AnchorId | null,
getAnchorId: (item: Item) => AnchorId | null,
options: { readonly anchorOffset?: number } = {},
): ChatListAnchoredEndSpace | undefined => {
if (anchorId === null) return undefined;
for (let index = items.length - 1; index >= 0; index -= 1) {
const item = items[index];
if (item !== undefined && getAnchorId(item) === anchorId) {
return {
anchorIndex: index,
anchorOffset: options.anchorOffset ?? CHAT_LIST_ANCHOR_OFFSET,
};
}
}
return undefined;
};
@@ -19,7 +19,7 @@ import { SaveProjectPlanDialog } from '@/components/session/SaveProjectPlanDialo
import { ForkSessionDialog, type ForkSessionExecution } from '@/components/session/ForkSessionDialog';
import { Tooltip, TooltipContent, TooltipTrigger } from '@/components/ui/tooltip';
import { ArrowsMerge } from '@/components/icons/ArrowsMerge';
import type { ContentChangeReason } from '@/hooks/useChatAutoFollow';
import type { ContentChangeReason } from '@/hooks/useChatTimelineScroll';
import { MarkdownImageGallery, SimpleMarkdownRenderer } from '../MarkdownRenderer';
import { useSessionUIStore } from '@/sync/session-ui-store';
@@ -2,7 +2,7 @@ import React from 'react';
import type { Part } from '@opencode-ai/sdk/v2';
import { MarkdownRenderer } from '../../MarkdownRenderer';
import type { StreamPhase, ToolPopupContent } from '../types';
import type { ContentChangeReason } from '@/hooks/useChatAutoFollow';
import type { ContentChangeReason } from '@/hooks/useChatTimelineScroll';
import { useStreamingTextThrottle } from '../../hooks/useStreamingTextThrottle';
import { resolveAssistantDisplayText, shouldRenderAssistantText } from './assistantTextVisibility';
import { streamPerfCount, streamPerfObserve } from '@/stores/utils/streamDebug';
@@ -1,6 +1,6 @@
import React from 'react';
import type { Part } from '@opencode-ai/sdk/v2';
import type { ContentChangeReason } from '@/hooks/useChatAutoFollow';
import type { ContentChangeReason } from '@/hooks/useChatTimelineScroll';
import { useUIStore } from '@/stores/useUIStore';
import { ReasoningTimelineBlock } from './ReasoningPart';
@@ -4,7 +4,7 @@ import { cn } from '@/lib/utils';
import type { TurnActivityRecord as TurnActivityPart } from '../../lib/turns/types';
import type { ToolPart as ToolPartType } from '@opencode-ai/sdk/v2';
import type { StreamPhase } from '../types';
import type { ContentChangeReason } from '@/hooks/useChatAutoFollow';
import type { ContentChangeReason } from '@/hooks/useChatTimelineScroll';
import type { ToolPopupContent } from '../types';
import ToolPart from './ToolPart';
import { MinDurationShineText } from './MinDurationShineText';
@@ -2,7 +2,7 @@ import React from 'react';
import { animate, type AnimationPlaybackControls } from 'motion';
import type { Part } from '@opencode-ai/sdk/v2';
import { cn } from '@/lib/utils';
import type { ContentChangeReason } from '@/hooks/useChatAutoFollow';
import type { ContentChangeReason } from '@/hooks/useChatTimelineScroll';
import { ScrollableOverlay } from '@/components/ui/ScrollableOverlay';
import { Icon } from '@/components/icon/Icon';
import { BusyDots } from './BusyDots';
@@ -20,7 +20,7 @@ import { toast } from '@/components/ui';
import { Text } from '@/components/ui/text';
import { FileTypeIcon } from '@/components/icons/FileTypeIcon';
import { copyTextToClipboard } from '@/lib/clipboard';
import type { ContentChangeReason } from '@/hooks/useChatAutoFollow';
import type { ContentChangeReason } from '@/hooks/useChatTimelineScroll';
import type { ToolPopupContent } from '../types';
import { PlainDiffFallback } from './PlainDiffFallback';
import { lazyWithChunkRecovery } from '@/lib/chunkLoadRecovery';
+13 -101
View File
@@ -1,15 +1,17 @@
import React from "react";
import { useScrollShadow, type ScrollShadowOrientation, type ScrollShadowVisibility } from "./useScrollShadow";
export type ScrollShadowProps = React.HTMLAttributes<HTMLElement> & {
as?: React.ElementType;
orientation?: "vertical" | "horizontal";
orientation?: ScrollShadowOrientation;
offset?: number;
size?: number;
isEnabled?: boolean;
hideTopShadow?: boolean;
hideBottomShadow?: boolean;
observeMutations?: boolean;
onVisibilityChange?: (state: "both" | "none" | "top" | "bottom" | "left" | "right") => void;
onVisibilityChange?: (state: ScrollShadowVisibility) => void;
};
function mergeRefs<T>(...refs: Array<React.Ref<T>>): React.RefCallback<T> {
@@ -44,7 +46,6 @@ export const ScrollShadow = React.forwardRef<HTMLElement, ScrollShadowProps>(
ref,
) => {
const internalRef = React.useRef<HTMLElement>(null);
const visibleRef = React.useRef<"both" | "none" | "top" | "bottom" | "left" | "right">("none");
const dataScrollShadow = (rest as Record<string, unknown>)["data-scroll-shadow"];
delete (rest as Record<string, unknown>)["data-scroll-shadow"];
@@ -57,104 +58,15 @@ export const ScrollShadow = React.forwardRef<HTMLElement, ScrollShadowProps>(
return next;
}, [size, style]);
const setAttributes = React.useCallback(
(el: HTMLElement, hasBefore: boolean, hasAfter: boolean, prefix: "top" | "left", suffix: "bottom" | "right") => {
const bothKey = `${prefix}${suffix.charAt(0).toUpperCase()}${suffix.slice(1)}Scroll` as const;
if (hasBefore && hasAfter) {
(el.dataset as Record<string, string>)[bothKey] = "true";
el.removeAttribute(`data-${prefix}-scroll`);
el.removeAttribute(`data-${suffix}-scroll`);
} else {
el.dataset[`${prefix}Scroll`] = String(hasBefore);
el.dataset[`${suffix}Scroll`] = String(hasAfter);
el.removeAttribute(`data-${prefix}-${suffix}-scroll`);
}
},
[],
);
const clearAttributes = React.useCallback((el: HTMLElement) => {
["top", "bottom", "top-bottom", "left", "right", "left-right"].forEach((attr) => {
el.removeAttribute(`data-${attr}-scroll`);
});
}, []);
const checkOverflow = React.useCallback(() => {
const el = internalRef.current;
if (!el) return;
if (!isEnabled) {
clearAttributes(el);
return;
}
// Subpixel tolerance: on hi-DPI (Retina) and with fractional scrollTop,
// scrollTop+clientHeight can fall ~0.5px short of scrollHeight at the very end,
// which would otherwise keep the bottom fade visible after fully scrolling.
const SUBPIXEL_TOLERANCE = 1;
const hasBefore =
orientation === "vertical"
? el.scrollTop > offset + SUBPIXEL_TOLERANCE
: el.scrollLeft > offset + SUBPIXEL_TOLERANCE;
let hasAfter =
orientation === "vertical"
? el.scrollHeight - (el.scrollTop + el.clientHeight) > offset + SUBPIXEL_TOLERANCE
: el.scrollWidth - (el.scrollLeft + el.clientWidth) > offset + SUBPIXEL_TOLERANCE;
const effectiveHasBefore = hideTopShadow && orientation === "vertical" ? false : hasBefore;
if (hideBottomShadow && orientation === "vertical") {
hasAfter = false;
}
setAttributes(el, effectiveHasBefore, hasAfter, orientation === "vertical" ? "top" : "left", orientation === "vertical" ? "bottom" : "right");
const next = effectiveHasBefore && hasAfter ? "both" : effectiveHasBefore ? (orientation === "vertical" ? "top" : "left") : hasAfter ? (orientation === "vertical" ? "bottom" : "right") : "none";
if (next !== visibleRef.current) {
visibleRef.current = next;
onVisibilityChange?.(next);
}
}, [clearAttributes, hideTopShadow, hideBottomShadow, isEnabled, offset, onVisibilityChange, orientation, setAttributes]);
React.useEffect(() => {
const el = internalRef.current;
if (!el) return;
// Throttle with RAF to avoid excessive calls during rapid DOM changes
let rafId: number | null = null;
const throttledCheck = () => {
if (rafId !== null) return;
rafId = requestAnimationFrame(() => {
rafId = null;
checkOverflow();
});
};
const handleScroll = () => checkOverflow(); // Scroll should be immediate
const resizeObserver = typeof ResizeObserver !== "undefined" ? new ResizeObserver(throttledCheck) : null;
const mutationObserver =
observeMutations && typeof MutationObserver !== "undefined" ? new MutationObserver(throttledCheck) : null;
checkOverflow();
el.addEventListener("scroll", handleScroll, { passive: true });
resizeObserver?.observe(el);
// checkOverflow mutates our data-scroll attributes; observing attributes
// would make the component trigger its own observer indefinitely.
mutationObserver?.observe(el, {
childList: true,
subtree: true,
characterData: true,
});
return () => {
if (rafId !== null) cancelAnimationFrame(rafId);
el.removeEventListener("scroll", handleScroll);
resizeObserver?.disconnect();
mutationObserver?.disconnect();
};
}, [checkOverflow, observeMutations]);
useScrollShadow(internalRef, {
orientation,
offset,
isEnabled,
hideTopShadow,
hideBottomShadow,
observeMutations,
onVisibilityChange,
});
return (
<Component
@@ -0,0 +1,159 @@
import React from "react";
// Scroll-shadow state as data attributes on a scroll container.
//
// The logic lives in a hook rather than only inside <ScrollShadow> because the
// chat timeline's scroll container is owned by the virtualized list component,
// which renders its own element — there is no wrapper to hand the styling to.
// <ScrollShadow> is a thin wrapper over this hook, so both paths stay in sync.
export type ScrollShadowOrientation = "vertical" | "horizontal";
export type ScrollShadowVisibility = "both" | "none" | "top" | "bottom" | "left" | "right";
export type UseScrollShadowOptions = {
orientation?: ScrollShadowOrientation;
offset?: number;
isEnabled?: boolean;
hideTopShadow?: boolean;
hideBottomShadow?: boolean;
observeMutations?: boolean;
onVisibilityChange?: (state: ScrollShadowVisibility) => void;
};
const SCROLL_SHADOW_ATTRIBUTES = [
"top",
"bottom",
"top-bottom",
"left",
"right",
"left-right",
] as const;
const clearScrollShadowAttributes = (el: HTMLElement): void => {
SCROLL_SHADOW_ATTRIBUTES.forEach((attr) => {
el.removeAttribute(`data-${attr}-scroll`);
});
};
const setScrollShadowAttributes = (
el: HTMLElement,
hasBefore: boolean,
hasAfter: boolean,
prefix: "top" | "left",
suffix: "bottom" | "right",
): void => {
const bothKey = `${prefix}${suffix.charAt(0).toUpperCase()}${suffix.slice(1)}Scroll` as const;
if (hasBefore && hasAfter) {
(el.dataset as Record<string, string>)[bothKey] = "true";
el.removeAttribute(`data-${prefix}-scroll`);
el.removeAttribute(`data-${suffix}-scroll`);
} else {
el.dataset[`${prefix}Scroll`] = String(hasBefore);
el.dataset[`${suffix}Scroll`] = String(hasAfter);
el.removeAttribute(`data-${prefix}-${suffix}-scroll`);
}
};
export const useScrollShadow = (
elementRef: React.RefObject<HTMLElement | null>,
{
orientation = "vertical",
offset = 0,
isEnabled = true,
hideTopShadow = false,
hideBottomShadow = false,
observeMutations = true,
onVisibilityChange,
}: UseScrollShadowOptions = {},
): void => {
const visibleRef = React.useRef<ScrollShadowVisibility>("none");
const checkOverflow = React.useCallback(() => {
const el = elementRef.current;
if (!el) return;
if (!isEnabled) {
clearScrollShadowAttributes(el);
return;
}
// Subpixel tolerance: on hi-DPI (Retina) and with fractional scrollTop,
// scrollTop+clientHeight can fall ~0.5px short of scrollHeight at the very end,
// which would otherwise keep the bottom fade visible after fully scrolling.
const SUBPIXEL_TOLERANCE = 1;
const hasBefore =
orientation === "vertical"
? el.scrollTop > offset + SUBPIXEL_TOLERANCE
: el.scrollLeft > offset + SUBPIXEL_TOLERANCE;
let hasAfter =
orientation === "vertical"
? el.scrollHeight - (el.scrollTop + el.clientHeight) > offset + SUBPIXEL_TOLERANCE
: el.scrollWidth - (el.scrollLeft + el.clientWidth) > offset + SUBPIXEL_TOLERANCE;
const effectiveHasBefore = hideTopShadow && orientation === "vertical" ? false : hasBefore;
if (hideBottomShadow && orientation === "vertical") {
hasAfter = false;
}
setScrollShadowAttributes(
el,
effectiveHasBefore,
hasAfter,
orientation === "vertical" ? "top" : "left",
orientation === "vertical" ? "bottom" : "right",
);
const next: ScrollShadowVisibility = effectiveHasBefore && hasAfter
? "both"
: effectiveHasBefore
? (orientation === "vertical" ? "top" : "left")
: hasAfter
? (orientation === "vertical" ? "bottom" : "right")
: "none";
if (next !== visibleRef.current) {
visibleRef.current = next;
onVisibilityChange?.(next);
}
}, [elementRef, hideTopShadow, hideBottomShadow, isEnabled, offset, onVisibilityChange, orientation]);
React.useEffect(() => {
const el = elementRef.current;
if (!el) return;
// Throttle with RAF to avoid excessive calls during rapid DOM changes
let rafId: number | null = null;
const throttledCheck = () => {
if (rafId !== null) return;
rafId = requestAnimationFrame(() => {
rafId = null;
checkOverflow();
});
};
const handleScroll = () => checkOverflow(); // Scroll should be immediate
const resizeObserver = typeof ResizeObserver !== "undefined" ? new ResizeObserver(throttledCheck) : null;
const mutationObserver =
observeMutations && typeof MutationObserver !== "undefined" ? new MutationObserver(throttledCheck) : null;
checkOverflow();
el.addEventListener("scroll", handleScroll, { passive: true });
resizeObserver?.observe(el);
// checkOverflow mutates our data-scroll attributes; observing attributes
// would make the hook trigger its own observer indefinitely.
mutationObserver?.observe(el, {
childList: true,
subtree: true,
characterData: true,
});
return () => {
if (rafId !== null) cancelAnimationFrame(rafId);
el.removeEventListener("scroll", handleScroll);
resizeObserver?.disconnect();
mutationObserver?.disconnect();
};
}, [checkOverflow, elementRef, observeMutations]);
};