11import type { TurbopackMessageAction } from '../../../../server/dev/hot-reloader-types'
22import type { Update as TurbopackUpdate } from '../../../../build/swc/types'
33
4+ declare global {
5+ interface Window {
6+ __NEXT_HMR_TURBOPACK_REPORT_NOISY_NOOP_EVENTS : boolean | undefined
7+ }
8+ }
9+
10+ // How long to wait before reporting the HMR start, used to suppress irrelevant
11+ // `BUILDING` events. Does not impact reported latency.
12+ const TURBOPACK_HMR_START_DELAY_MS = 100
13+
414interface HmrUpdate {
15+ hasUpdates : boolean
516 updatedModules : Set < string >
617 startMsSinceEpoch : number
718 endMsSinceEpoch : number
@@ -11,17 +22,51 @@ export class TurbopackHmr {
1122 #updatedModules: Set < string >
1223 #startMsSinceEpoch: number | undefined
1324 #lastUpdateMsSinceEpoch: number | undefined
25+ #deferredReportHmrStartId: ReturnType < typeof setTimeout > | undefined
1426
1527 constructor ( ) {
1628 this . #updatedModules = new Set ( )
1729 }
1830
31+ // HACK: Turbopack tends to generate a lot of irrelevant "BUILDING" actions,
32+ // as it reports *any* compilation, including fully no-op/cached compilations
33+ // and those unrelated to HMR. Fixing this would require significant
34+ // architectural changes.
35+ //
36+ // Work around this by deferring any "rebuilding" message by 100ms. If we get
37+ // a BUILT event within that threshold and nothing has changed, just suppress
38+ // the message entirely.
39+ #runDeferredReportHmrStart( ) {
40+ if ( this . #deferredReportHmrStartId != null ) {
41+ console . log ( '[Fast Refresh] rebuilding' )
42+ this . #cancelDeferredReportHmrStart( )
43+ }
44+ }
45+
46+ #cancelDeferredReportHmrStart( ) {
47+ clearTimeout ( this . #deferredReportHmrStartId)
48+ this . #deferredReportHmrStartId = undefined
49+ }
50+
1951 onBuilding ( ) {
2052 this . #lastUpdateMsSinceEpoch = undefined
53+ this . #cancelDeferredReportHmrStart( )
2154 this . #startMsSinceEpoch = Date . now ( )
55+
56+ if ( self . __NEXT_HMR_TURBOPACK_REPORT_NOISY_NOOP_EVENTS ) {
57+ // debugging feature: don't defer/suppress noisy no-op HMR update messages
58+ this . #runDeferredReportHmrStart( )
59+ } else {
60+ // report the HMR start after a short delay
61+ this . #deferredReportHmrStartId = setTimeout (
62+ ( ) => this . #runDeferredReportHmrStart( ) ,
63+ TURBOPACK_HMR_START_DELAY_MS
64+ )
65+ }
2266 }
2367
2468 onTurbopackMessage ( msg : TurbopackMessageAction ) {
69+ this . #runDeferredReportHmrStart( )
2570 this . #lastUpdateMsSinceEpoch = Date . now ( )
2671 const updatedModules = extractModulesFromTurbopackMessage ( msg . data )
2772 for ( const module of updatedModules ) {
@@ -30,25 +75,31 @@ export class TurbopackHmr {
3075 }
3176
3277 onBuilt ( ) : HmrUpdate | null {
33- // it's possible for `this.#startMsSinceEpoch` to not be set if this was the initial
34- // computation, just return null in this case.
35- if ( this . #startMsSinceEpoch == null ) {
78+ // Check that we got *any* `TurbopackMessageAction`, even if `updatedModules` is empty (not
79+ // everything gets recorded there).
80+ //
81+ // This also handles for the case where `onBuilt` gets called before `onBuilding`, which can
82+ // happen during initial page load. We should ignore this.
83+ const hasUpdates = this . #lastUpdateMsSinceEpoch != null
84+ if ( ! hasUpdates && this . #deferredReportHmrStartId != null ) {
85+ // suppress the update entirely
86+ this . #cancelDeferredReportHmrStart( )
3687 return null
3788 }
89+ this . #runDeferredReportHmrStart( )
90+
3891 const result = {
92+ hasUpdates,
3993 updatedModules : this . #updatedModules,
4094 startMsSinceEpoch : this . #startMsSinceEpoch! ,
41- // Turbopack has a debounce which causes every BUILT message to appear
42- // 30ms late. We don't want to include this latency in our reporting, so
43- // prefer to use the last TURBOPACK_MESSAGE time.
4495 endMsSinceEpoch : this . #lastUpdateMsSinceEpoch ?? Date . now ( ) ,
4596 }
4697 this . #updatedModules = new Set ( )
4798 return result
4899 }
49100}
50101
51- export function extractModulesFromTurbopackMessage (
102+ function extractModulesFromTurbopackMessage (
52103 data : TurbopackUpdate | TurbopackUpdate [ ]
53104) : Set < string > {
54105 const updatedModules : Set < string > = new Set ( )
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