Use fork-sync for Folly and FastFloat

[vmoroz]

Description

Type of Change

• New feature (non-breaking change which adds functionality)

Why

This is Phase 2 of the fork-sync migration (Phase 1 PR landed fmt). Currently, Folly and FastFloat sources are downloaded at build time from GitHub, unzipped into node_modules/, and then patched in-place. This approach is fragile, makes offline builds impossible, and hides the actual source code that ships in the binary.

By committing the vendored source directly — with patches already applied — we get:

• Reproducible builds — no network dependency for third-party source
• Visible patches — Windows-specific changes are in the committed tree, reviewable in normal diffs
• Simpler build — no download/unzip/patch targets; sources compile via shared .vcxitems
• Automated sync — @rnx-kit/fork-sync can update to new upstream versions and flag merge conflicts with our patches

What

Folly 2024.10.14.00 committed into vnext/external/folly/ (797 files, ~9 MB):

• Full source trimmed to only the 12 subdirectories RNW actually uses (chrono, concurrency, container, detail, functional, hash, json, lang, memory, portability, synchronization, system) plus algorithm/simd/
• 33 unused subdirectories excluded via .syncignore (coro, executors, fibers, futures, io, logging, etc.)
• 10 Windows patches from TEMP_UntilFollyUpdate/ applied in-place
• folly.vcxitems with 30 ClCompile entries, PCH support, Desktop-only SysMman.cpp
• Object filename overrides to avoid collisions (folly_pch.obj, folly_Format.obj, portabilityString.obj)

FastFloat 8.0.0 committed into vnext/external/fast-float/ (13 files, header-only):

• fast-float.vcxitems with ClInclude entries only

Build system changes:

• React.Cpp.props — include paths changed from $(FollyDir) / $(FastFloatDir) to $(ExternalDir)folly / $(ExternalDir)fast-float\include
• Directory.Build.props — removed 6 properties: FollyVersion, FastFloatVersion, FollyCommitHash, FastFloatCommitHash, FollyDir, FastFloatDir
• External.vcxitems — imports folly.vcxitems and fast-float.vcxitems
• Layout-Desktop-Headers.ps1 — uses committed source; removed download logic and override section

Cleanup:

• Deleted vnext/Folly/Folly.vcxproj, .vcxproj.filters, cgmanifest.json, .clang-format, packages.lock.json
• Deleted vnext/Folly/TEMP_UntilFollyUpdate/ (patches now in-place)
• Deleted vnext/FollyWin32/ entirely (SysMman.cpp now in folly.vcxitems with AppContainerApplication condition)
• Moved Folly.natvis to vnext/external/folly/
• Kept vnext/Folly/pch.h, pch.cpp, ThreadNameStub.cpp (RNW-specific, referenced from vcxitems)
• Removed Folly/FollyWin32 from 12 .sln files, 2 .slnf files
• Removed ProjectReference to Folly from 4 .vcxproj files (Microsoft.ReactNative, ReactCommon, Desktop, IntegrationTests)
• Updated sync-manifest.json with folly and fast-float entries
• Added DisableFormat: true .clang-format inside folly/folly/ to prevent yarn format from reformatting vendored code

Screenshots

N/A — build infrastructure change, no UI impact.

Testing

• Built Microsoft.ReactNative.vcxproj (Debug|x64) — all Folly sources compile via vcxitems chain, links successfully into Microsoft.ReactNative.dll
• Built React.Windows.Desktop.DLL.vcxproj (Debug|x64) — SysMman.cpp compiles for Desktop, links into react-native-win32.dll
• Verified no stale references to $(FollyDir), $(FastFloatDir), FollyVersion, FastFloatVersion, FollyCommitHash, FastFloatCommitHash remain in build files
• Verified Folly.vcxproj is removed from all solutions

Changelog

Should this change be included in the release notes: no
Internal build infrastructure change — no API or behavior changes.

Microsoft Reviewers: Open in CodeFlow

[github-actions]

Performance Test Results

Branch: PR/fork-sync-folly
Commit: d04d75ca
Time: 2026-04-10T18:27:50.126Z
Tests: 161/161 passed

✅ Passed

161 scenario(s) across 28 suite(s) — no regressions

SectionList

Scenario	Mean	Median	StdDev	Renders	vs Baseline
SectionList mount	4.50ms	4.00ms	±2.07ms	1	-20.0%
SectionList unmount	0.00ms	0.00ms	±0.00ms	0	+0.0%
SectionList rerender	11.50ms	11.00ms	±2.27ms	2	+4.8%
SectionList with-3-sections-15-items	5.40ms	5.50ms	±1.17ms	1	+0.0%
SectionList with-5-sections-50-items	5.10ms	5.00ms	±0.74ms	1	-16.7%
SectionList with-10-sections-200-items	4.90ms	4.50ms	±1.29ms	1	-18.2%
SectionList with-20-sections-200-items	5.60ms	4.50ms	±2.88ms	1	-10.0%
SectionList with-section-separator	2.80ms	3.00ms	±0.63ms	1	+50.0%
SectionList with-item-separator	3.00ms	2.50ms	±1.76ms	1	+25.0%
SectionList with-header-footer	2.00ms	2.00ms	±0.67ms	1	+0.0%
SectionList with-section-footer	1.50ms	1.50ms	±0.53ms	1	-25.0%
SectionList with-sticky-section-headers	1.60ms	1.00ms	±0.97ms	1	-50.0%
SectionList with-empty-list	0.30ms	0.00ms	±0.48ms	1	-100.0%
SectionList with-50-sections-1000-items	1.70ms	2.00ms	±0.48ms	1	+0.0%

FlatList

Scenario	Mean	Median	StdDev	Renders	vs Baseline
FlatList mount	4.40ms	4.00ms	±0.70ms	1	+0.0%
FlatList unmount	0.20ms	0.00ms	±0.42ms	0	+0.0%
FlatList rerender	10.20ms	10.00ms	±1.93ms	2	+11.1%
FlatList with-10-items	4.50ms	4.00ms	±0.97ms	1	+0.0%
FlatList with-100-items	5.20ms	5.00ms	±1.62ms	1	+0.0%
FlatList with-500-items	5.40ms	5.50ms	±1.17ms	1	+37.5%
FlatList with-1000-items	4.70ms	4.00ms	±1.70ms	1	+0.0%
FlatList horizontal	4.00ms	4.00ms	±1.25ms	1	-20.0%
FlatList with-separator	1.90ms	1.50ms	±1.52ms	1	-25.0%
FlatList with-header-footer	1.20ms	1.00ms	±0.42ms	1	-50.0%
FlatList with-empty-list	0.40ms	0.00ms	±0.52ms	1	-100.0%
FlatList with-get-item-layout	1.50ms	1.50ms	±0.53ms	1	+50.0%
FlatList inverted	1.30ms	1.00ms	±0.48ms	1	-33.3%
FlatList with-num-columns	2.50ms	2.50ms	±0.53ms	1	-16.7%

TouchableOpacity

Scenario	Mean	Median	StdDev	Renders	vs Baseline
TouchableOpacity mount	0.90ms	1.00ms	±0.32ms	1	+0.0%
TouchableOpacity unmount	0.00ms	0.00ms	±0.00ms	0	+0.0%
TouchableOpacity rerender	1.90ms	2.00ms	±0.32ms	2	+100.0%
TouchableOpacity custom-active-opacity	0.50ms	0.50ms	±0.53ms	1	-50.0%
TouchableOpacity disabled	0.70ms	1.00ms	±0.48ms	1	+0.0%
TouchableOpacity with-all-handlers	0.70ms	1.00ms	±0.48ms	1	+0.0%
TouchableOpacity with-hit-slop	0.90ms	1.00ms	±0.57ms	1	+0.0%
TouchableOpacity with-delay	0.40ms	0.00ms	±0.52ms	1	-100.0%
TouchableOpacity nested	1.20ms	1.00ms	±0.42ms	1	+0.0%
TouchableOpacity multiple-10	5.80ms	5.00ms	±2.60ms	1	-16.7%
TouchableOpacity multiple-50	25.40ms	25.00ms	±3.20ms	1	-13.8%
TouchableOpacity multiple-100	31.73ms	27.00ms	±13.54ms	1	-46.0%

ScrollView

Scenario	Mean	Median	StdDev	Renders	vs Baseline
ScrollView mount	0.30ms	0.00ms	±0.48ms	1	+0.0%
ScrollView unmount	0.10ms	0.00ms	±0.32ms	0	+0.0%
ScrollView rerender	0.50ms	0.00ms	±0.71ms	2	-100.0%
ScrollView children-20	2.87ms	3.00ms	±0.64ms	1	-25.0%
ScrollView children-100	17.07ms	16.00ms	±3.90ms	1	+0.0%
ScrollView horizontal	3.60ms	3.00ms	±0.84ms	1	-25.0%
ScrollView sticky-headers	2.50ms	3.00ms	±0.85ms	1	+0.0%
ScrollView scroll-indicators	0.60ms	1.00ms	±0.52ms	1	+0.0%
ScrollView nested	1.40ms	1.00ms	±0.70ms	1	+0.0%
ScrollView content-container-style	0.90ms	1.00ms	±0.32ms	1	+0.0%
ScrollView children-500	21.40ms	21.00ms	±5.26ms	1	+10.5%

TouchableHighlight

Scenario	Mean	Median	StdDev	Renders	vs Baseline
TouchableHighlight mount	0.40ms	0.00ms	±0.52ms	1	-100.0%
TouchableHighlight unmount	0.00ms	0.00ms	±0.00ms	0	+0.0%
TouchableHighlight rerender	0.70ms	1.00ms	±0.48ms	2	+0.0%
TouchableHighlight custom-underlay-color	0.30ms	0.00ms	±0.48ms	1	+0.0%
TouchableHighlight custom-active-opacity	0.90ms	0.50ms	±1.52ms	1	+Infinity%
TouchableHighlight disabled	0.30ms	0.00ms	±0.48ms	1	+0.0%
TouchableHighlight with-all-handlers	0.20ms	0.00ms	±0.42ms	1	+0.0%
TouchableHighlight with-hit-slop	0.30ms	0.00ms	±0.48ms	1	+0.0%
TouchableHighlight nested-touchables	0.90ms	1.00ms	±0.32ms	1	+0.0%
TouchableHighlight multiple-touchables-10	3.10ms	3.00ms	±0.74ms	1	+0.0%
TouchableHighlight multiple-touchables-50	12.30ms	12.00ms	±2.06ms	1	-4.0%
TouchableHighlight multiple-touchables-100	23.80ms	22.50ms	±4.08ms	1	+0.0%

Pressable

Scenario	Mean	Median	StdDev	Renders	vs Baseline
Pressable mount	0.40ms	0.00ms	±0.52ms	1	+0.0%
Pressable unmount	0.00ms	0.00ms	±0.00ms	0	+0.0%
Pressable rerender	0.50ms	0.50ms	±0.53ms	2	+0.0%
Pressable with-all-handlers	0.40ms	0.00ms	±0.52ms	1	+0.0%
Pressable with-style-function	0.20ms	0.00ms	±0.42ms	1	+0.0%
Pressable disabled	0.40ms	0.00ms	±0.52ms	1	+0.0%
Pressable with-hit-slop	0.30ms	0.00ms	±0.48ms	1	+0.0%
Pressable nested	0.60ms	1.00ms	±0.52ms	1	+0.0%
Pressable multiple-10	2.93ms	3.00ms	±0.70ms	1	+0.0%
Pressable multiple-50	19.27ms	16.00ms	±12.24ms	1	+14.3%
Pressable multiple-100	19.53ms	11.00ms	±15.80ms	1	-8.3%

Modal

Scenario	Mean	Median	StdDev	Renders	vs Baseline
Modal mount	0.20ms	0.00ms	±0.42ms	1	+0.0%
Modal unmount	0.00ms	0.00ms	±0.00ms	0	+0.0%
Modal rerender	0.20ms	0.00ms	±0.42ms	2	+0.0%
Modal slide-animation	0.20ms	0.00ms	±0.42ms	1	+0.0%
Modal fade-animation	0.30ms	0.00ms	±0.48ms	1	+0.0%
Modal transparent	0.30ms	0.00ms	±0.48ms	1	+0.0%
Modal with-callbacks	0.10ms	0.00ms	±0.32ms	1	+0.0%
Modal rich-content	1.90ms	2.00ms	±0.74ms	1	+0.0%
Modal with-accessibility	0.30ms	0.00ms	±0.48ms	1	+0.0%

Image

Scenario	Mean	Median	StdDev	Renders	vs Baseline
Image mount	0.00ms	0.00ms	±0.00ms	1	+0.0%
Image unmount	0.00ms	0.00ms	±0.00ms	0	+0.0%
Image rerender	0.10ms	0.00ms	±0.32ms	2	+0.0%
Image with-resize-mode	0.30ms	0.00ms	±0.48ms	1	+0.0%
Image with-border-radius	0.20ms	0.00ms	±0.42ms	1	+0.0%
Image with-tint-color	0.10ms	0.00ms	±0.32ms	1	+0.0%
Image with-blur-radius	0.10ms	0.00ms	±0.32ms	1	+0.0%
Image with-accessibility	0.20ms	0.00ms	±0.42ms	1	+0.0%
Image multiple-10	0.87ms	1.00ms	±0.35ms	1	+0.0%
Image multiple-50	3.27ms	3.00ms	±0.59ms	1	+0.0%
Image multiple-100	8.20ms	7.00ms	±1.74ms	1	-12.5%

ActivityIndicator

Scenario	Mean	Median	StdDev	Renders	vs Baseline
ActivityIndicator mount	0.10ms	0.00ms	±0.32ms	1	+0.0%
ActivityIndicator unmount	0.10ms	0.00ms	±0.32ms	0	+0.0%
ActivityIndicator rerender	0.00ms	0.00ms	±0.00ms	2	+0.0%
ActivityIndicator size-large	0.20ms	0.00ms	±0.42ms	1	+0.0%
ActivityIndicator size-small	0.20ms	0.00ms	±0.42ms	1	+0.0%
ActivityIndicator with-color	0.10ms	0.00ms	±0.32ms	1	+0.0%
ActivityIndicator not-animating	0.20ms	0.00ms	±0.42ms	1	+0.0%
ActivityIndicator with-accessibility	0.10ms	0.00ms	±0.32ms	1	+0.0%
ActivityIndicator multiple-10	0.87ms	1.00ms	±0.35ms	1	+0.0%
ActivityIndicator multiple-50	3.40ms	3.00ms	±0.83ms	1	-25.0%
ActivityIndicator multiple-100	8.27ms	8.00ms	±1.94ms	1	+14.3%

Switch

Scenario	Mean	Median	StdDev	Renders	vs Baseline
Switch mount	0.20ms	0.00ms	±0.42ms	1	+0.0%
Switch unmount	0.00ms	0.00ms	±0.00ms	0	+0.0%
Switch rerender	0.30ms	0.00ms	±0.48ms	2	-100.0%
Switch value-true	0.30ms	0.00ms	±0.48ms	1	+0.0%
Switch disabled	0.20ms	0.00ms	±0.42ms	1	+0.0%
Switch custom-colors	0.30ms	0.00ms	±0.48ms	1	+0.0%
Switch on-value-change	0.20ms	0.00ms	±0.42ms	1	+0.0%
Switch with-accessibility	0.30ms	0.00ms	±0.48ms	1	+0.0%
Switch multiple-10	1.33ms	1.00ms	±0.49ms	1	-50.0%
Switch multiple-50	8.80ms	7.00ms	±2.76ms	1	-22.2%
Switch multiple-100	18.00ms	18.00ms	±4.39ms	1	+12.5%

Button

Scenario	Mean	Median	StdDev	Renders	vs Baseline
Button mount	0.50ms	0.50ms	±0.53ms	1	-50.0%
Button unmount	0.00ms	0.00ms	±0.00ms	0	+0.0%
Button rerender	1.10ms	1.00ms	±0.32ms	2	+0.0%
Button disabled	0.50ms	0.50ms	±0.53ms	1	-50.0%
Button with-color	0.70ms	1.00ms	±0.48ms	1	+100.0%
Button with-accessibility	0.50ms	0.50ms	±0.53ms	1	-50.0%
Button multiple-10	5.73ms	5.00ms	±1.83ms	1	-16.7%
Button multiple-50	21.40ms	23.00ms	±7.27ms	1	-14.8%
Button multiple-100	15.73ms	16.00ms	±3.83ms	1	-15.8%

TextInput

Scenario	Mean	Median	StdDev	Renders	vs Baseline
TextInput mount	0.20ms	0.00ms	±0.42ms	1	+0.0%
TextInput unmount	0.00ms	0.00ms	±0.00ms	0	+0.0%
TextInput rerender	0.30ms	0.00ms	±0.48ms	2	+0.0%
TextInput multiline	0.10ms	0.00ms	±0.32ms	1	+0.0%
TextInput with-value	0.20ms	0.00ms	±0.42ms	1	+0.0%
TextInput styled	0.20ms	0.00ms	±0.42ms	1	+0.0%
TextInput multiple-100	7.87ms	7.00ms	±2.23ms	1	+0.0%

View

Scenario	Mean	Median	StdDev	Renders	vs Baseline
View mount	0.20ms	0.00ms	±0.42ms	1	+0.0%
View unmount	0.00ms	0.00ms	±0.00ms	0	+0.0%
View rerender	0.30ms	0.00ms	±0.48ms	2	+0.0%
View nested-50	3.20ms	3.00ms	±0.41ms	1	+0.0%
View nested-100	8.27ms	7.00ms	±2.15ms	1	+0.0%
View shadow	0.20ms	0.00ms	±0.42ms	1	+0.0%
View border-radius	0.20ms	0.00ms	±0.42ms	1	+0.0%
View nested-500	18.33ms	11.00ms	±14.39ms	1	+10.0%

Text

Scenario	Mean	Median	StdDev	Renders	vs Baseline
Text mount	0.20ms	0.00ms	±0.42ms	1	+0.0%
Text unmount	0.00ms	0.00ms	±0.00ms	0	+0.0%
Text rerender	0.10ms	0.00ms	±0.32ms	2	+0.0%
Text long-1000	0.10ms	0.00ms	±0.32ms	1	+0.0%
Text nested	0.30ms	0.00ms	±0.48ms	1	+0.0%
Text styled	0.10ms	0.00ms	±0.32ms	1	+0.0%
Text multiple-100	7.73ms	7.00ms	±1.71ms	1	+0.0%

SectionList.native-perf-test.ts

Scenario	Mean	Median	StdDev	Renders	vs Baseline
SectionList native mount	6.48ms	6.10ms	±1.16ms	1	-6.1%

FlatList.native-perf-test.ts

Scenario	Mean	Median	StdDev	Renders	vs Baseline
FlatList native mount	5.84ms	5.71ms	±1.00ms	1	-38.1%

TouchableHighlight.native-perf-test.ts

Scenario	Mean	Median	StdDev	Renders	vs Baseline
TouchableHighlight native mount	1.81ms	1.76ms	±0.20ms	1	-15.7%

TouchableOpacity.native-perf-test.ts

Scenario	Mean	Median	StdDev	Renders	vs Baseline
TouchableOpacity native mount	2.40ms	2.41ms	±0.39ms	1	-23.1%

Pressable.native-perf-test.ts

Scenario	Mean	Median	StdDev	Renders	vs Baseline
Pressable native mount	2.10ms	1.86ms	±0.82ms	1	-25.8%

ScrollView.native-perf-test.ts

Scenario	Mean	Median	StdDev	Renders	vs Baseline
ScrollView native mount	5.54ms	5.44ms	±0.74ms	1	+34.3%

ActivityIndicator.native-perf-test.ts

Scenario	Mean	Median	StdDev	Renders	vs Baseline
ActivityIndicator native mount	1.60ms	1.50ms	±0.27ms	1	-39.5%

TextInput.native-perf-test.ts

Scenario	Mean	Median	StdDev	Renders	vs Baseline
TextInput native mount	2.28ms	2.23ms	±0.22ms	1	-45.4%

Switch.native-perf-test.ts

Scenario	Mean	Median	StdDev	Renders	vs Baseline
Switch native mount	1.44ms	1.36ms	±0.24ms	1	-21.8%

Button.native-perf-test.ts

Scenario	Mean	Median	StdDev	Renders	vs Baseline
Button native mount	2.13ms	2.07ms	±0.32ms	1	-20.6%

Modal.native-perf-test.ts

Scenario	Mean	Median	StdDev	Renders	vs Baseline
Modal native mount	1.36ms	1.30ms	±0.35ms	1	+7.1%

Image.native-perf-test.ts

Scenario	Mean	Median	StdDev	Renders	vs Baseline
Image native mount	2.30ms	2.10ms	±0.73ms	1	-6.9%

View.native-perf-test.ts

Scenario	Mean	Median	StdDev	Renders	vs Baseline
View native mount	1.50ms	1.39ms	±0.43ms	1	-2.8%

Text.native-perf-test.ts

Scenario	Mean	Median	StdDev	Renders	vs Baseline
Text native mount	1.58ms	1.53ms	±0.24ms	1	-12.1%