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fix: optimize ChatView to prevent excessive re-rendering when typing #7420

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fix: optimize ChatView to prevent excessive re-rendering when typing #7420

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1 change: 1 addition & 0 deletions webview-ui/src/components/chat/ChatRow.tsx
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Original file line number Diff line number Diff line change
Expand Up @@ -68,6 +68,7 @@ interface ChatRowContentProps extends Omit<ChatRowProps, "onHeightChange"> {}
const ChatRow = memo(
(props: ChatRowProps) => {
const { isLast, onHeightChange, message } = props

// Store the previous height to compare with the current height
// This allows us to detect changes without causing re-renders
const prevHeightRef = useRef(0)
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20 changes: 13 additions & 7 deletions webview-ui/src/components/chat/ChatView.tsx
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Original file line number Diff line number Diff line change
Expand Up @@ -160,7 +160,9 @@ const ChatViewComponent: React.ForwardRefRenderFunction<ChatViewRef, ChatViewPro
return getLatestTodo(messages)
}, [messages, currentTaskTodos])

const modifiedMessages = useMemo(() => combineApiRequests(combineCommandSequences(messages.slice(1))), [messages])
const modifiedMessages = useMemo(() => {
return combineApiRequests(combineCommandSequences(messages.slice(1)))
}, [messages])

// Has to be after api_req_finished are all reduced into api_req_started messages.
const apiMetrics = useMemo(() => getApiMetrics(modifiedMessages), [modifiedMessages])
Expand Down Expand Up @@ -1521,6 +1523,10 @@ const ChatViewComponent: React.ForwardRefRenderFunction<ChatViewRef, ChatViewPro
userRespondedRef.current = true
}, [])

// Memoize the last modified message to prevent unnecessary re-renders
const lastModifiedMessage = useMemo(() => modifiedMessages.at(-1), [modifiedMessages])
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@roomote roomote bot Aug 26, 2025

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While this memoization correctly prevents re-renders, I'm wondering if creating a new reference on every modifiedMessages change could lead to memory pressure in long-running sessions? Could we consider using a more granular dependency or perhaps a ref-based approach to track just the last message without triggering re-renders?


// Properly memoized itemContent callback with stable dependencies
const itemContent = useCallback(
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@roomote roomote bot Aug 26, 2025

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Since this is a performance fix, would it be helpful to add a comment documenting the performance improvement achieved? For example: "Reduces re-renders from X to Y when typing". Future me would appreciate knowing why past me made this change.

(index: number, messageOrGroup: ClineMessage | ClineMessage[]) => {
// browser session group
Expand All @@ -1529,7 +1535,7 @@ const ChatViewComponent: React.ForwardRefRenderFunction<ChatViewRef, ChatViewPro
<BrowserSessionRow
messages={messageOrGroup}
isLast={index === groupedMessages.length - 1}
lastModifiedMessage={modifiedMessages.at(-1)}
lastModifiedMessage={lastModifiedMessage}
onHeightChange={handleRowHeightChange}
isStreaming={isStreaming}
isExpanded={(messageTs: number) => expandedRows[messageTs] ?? false}
Expand All @@ -1549,12 +1555,12 @@ const ChatViewComponent: React.ForwardRefRenderFunction<ChatViewRef, ChatViewPro
key={messageOrGroup.ts}
message={messageOrGroup}
isExpanded={expandedRows[messageOrGroup.ts] || false}
onToggleExpand={toggleRowExpansion} // This was already stabilized
lastModifiedMessage={modifiedMessages.at(-1)} // Original direct access
isLast={index === groupedMessages.length - 1} // Original direct access
onToggleExpand={toggleRowExpansion}
lastModifiedMessage={lastModifiedMessage}
isLast={index === groupedMessages.length - 1}
onHeightChange={handleRowHeightChange}
isStreaming={isStreaming}
onSuggestionClick={handleSuggestionClickInRow} // This was already stabilized
onSuggestionClick={handleSuggestionClickInRow}
onBatchFileResponse={handleBatchFileResponse}
onFollowUpUnmount={handleFollowUpUnmount}
isFollowUpAnswered={messageOrGroup.ts === currentFollowUpTs}
Expand Down Expand Up @@ -1582,7 +1588,7 @@ const ChatViewComponent: React.ForwardRefRenderFunction<ChatViewRef, ChatViewPro
[
expandedRows,
toggleRowExpansion,
modifiedMessages,
lastModifiedMessage, // Use the memoized value instead of recalculating
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@roomote roomote bot Aug 26, 2025

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Could we add a comment explaining why switching from modifiedMessages to lastModifiedMessage in the dependency array prevents the re-rendering issue? The fix works, but documenting the reasoning would help future maintainers understand the optimization.

groupedMessages.length,
handleRowHeightChange,
isStreaming,
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