feat: make AssistantMessageParser an experimental feature

- Add assistantMessageParser experiment flag (disabled by default)
- When experiment is off, use the original parseAssistantMessage function
- When experiment is on, use the new AssistantMessageParser class
- Ensures backward compatibility with no behavior changes when disabled
- All existing tests pass with the experimental flag off

Author: daniel-lxs

packages/types/src/experiment.ts

@@ -6,7 +6,7 @@ import type { Keys, Equals, AssertEqual } from "./type-fu.js"
  * ExperimentId
  */
 
-export const experimentIds = ["powerSteering", "multiFileApplyDiff", "preventFocusDisruption"] as const
+export const experimentIds = ["powerSteering", "multiFileApplyDiff", "preventFocusDisruption", "assistantMessageParser"] as const
 
 export const experimentIdsSchema = z.enum(experimentIds)
 
@@ -20,6 +20,7 @@ export const experimentsSchema = z.object({
 	powerSteering: z.boolean().optional(),
 	multiFileApplyDiff: z.boolean().optional(),
 	preventFocusDisruption: z.boolean().optional(),
+	assistantMessageParser: z.boolean().optional(),
 })
 
 export type Experiments = z.infer<typeof experimentsSchema>

src/core/task/Task.ts

@@ -72,7 +72,7 @@ import { ToolRepetitionDetector } from "../tools/ToolRepetitionDetector"
 import { FileContextTracker } from "../context-tracking/FileContextTracker"
 import { RooIgnoreController } from "../ignore/RooIgnoreController"
 import { RooProtectedController } from "../protect/RooProtectedController"
-import { type AssistantMessageContent, presentAssistantMessage } from "../assistant-message"
+import { type AssistantMessageContent, presentAssistantMessage, parseAssistantMessage } from "../assistant-message"
 import { AssistantMessageParser } from "../assistant-message/AssistantMessageParser"
 import { truncateConversationIfNeeded } from "../sliding-window"
 import { ClineProvider } from "../webview/ClineProvider"
@@ -261,7 +261,8 @@ export class Task extends EventEmitter<TaskEvents> {
 	didRejectTool = false
 	didAlreadyUseTool = false
 	didCompleteReadingStream = false
-	assistantMessageParser = new AssistantMessageParser()
+	assistantMessageParser?: AssistantMessageParser
+	isAssistantMessageParserEnabled = false
 
 	constructor({
 		provider,
@@ -1536,7 +1537,9 @@ export class Task extends EventEmitter<TaskEvents> {
 			this.didAlreadyUseTool = false
 			this.presentAssistantMessageLocked = false
 			this.presentAssistantMessageHasPendingUpdates = false
-			this.assistantMessageParser.reset()
+			if (this.assistantMessageParser) {
+				this.assistantMessageParser.reset()
+			}
 
 			await this.diffViewProvider.reset()
 
@@ -1573,7 +1576,12 @@ export class Task extends EventEmitter<TaskEvents> {
 
 							// Parse raw assistant message chunk into content blocks.
 							const prevLength = this.assistantMessageContent.length
-							this.assistantMessageContent = this.assistantMessageParser.processChunk(chunk.text)
+							if (this.isAssistantMessageParserEnabled && this.assistantMessageParser) {
+								this.assistantMessageContent = this.assistantMessageParser.processChunk(chunk.text)
+							} else {
+								// Use the old parsing method when experiment is disabled
+								this.assistantMessageContent = parseAssistantMessage(assistantMessage)
+							}
 
 							if (this.assistantMessageContent.length > prevLength) {
 								// New content we need to present, reset to
@@ -1694,8 +1702,13 @@ export class Task extends EventEmitter<TaskEvents> {
 			// this.assistantMessageContent.forEach((e) => (e.partial = false))
 
 			// Now that the stream is complete, finalize any remaining partial content blocks
-			this.assistantMessageParser.finalizeContentBlocks()
-			this.assistantMessageContent = this.assistantMessageParser.getContentBlocks()
+			if (this.isAssistantMessageParserEnabled && this.assistantMessageParser) {
+				this.assistantMessageParser.finalizeContentBlocks()
+				this.assistantMessageContent = this.assistantMessageParser.getContentBlocks()
+			} else {
+				// When using old parser, parse the complete message
+				this.assistantMessageContent = parseAssistantMessage(assistantMessage)
+			}
 
 			if (partialBlocks.length > 0) {
 				// If there is content to update then it will complete and
@@ -1711,7 +1724,9 @@ export class Task extends EventEmitter<TaskEvents> {
 			await this.providerRef.deref()?.postStateToWebview()
 
 			// Reset parser after each complete conversation round
-			this.assistantMessageParser.reset()
+			if (this.assistantMessageParser) {
+				this.assistantMessageParser.reset()
+			}
 
 			// Now add to apiConversationHistory.
 			// Need to save assistant responses to file before proceeding to

src/shared/experiments.ts

@@ -4,6 +4,7 @@ export const EXPERIMENT_IDS = {
 	MULTI_FILE_APPLY_DIFF: "multiFileApplyDiff",
 	POWER_STEERING: "powerSteering",
 	PREVENT_FOCUS_DISRUPTION: "preventFocusDisruption",
+	ASSISTANT_MESSAGE_PARSER: "assistantMessageParser",
 } as const satisfies Record<string, ExperimentId>
 
 type _AssertExperimentIds = AssertEqual<Equals<ExperimentId, Values<typeof EXPERIMENT_IDS>>>
@@ -18,6 +19,7 @@ export const experimentConfigsMap: Record<ExperimentKey, ExperimentConfig> = {
 	MULTI_FILE_APPLY_DIFF: { enabled: false },
 	POWER_STEERING: { enabled: false },
 	PREVENT_FOCUS_DISRUPTION: { enabled: false },
+	ASSISTANT_MESSAGE_PARSER: { enabled: false },
 }
 
 export const experimentDefault = Object.fromEntries(