Case study: Bluesky social-app

To test Hozo against a real production React Native codebase rather than synthetic benchmarks, the repository pins a checkout of Bluesky’s bluesky-social/social-app (007c893de107c2ecbf2188d618196075f19c8f5a) and runs two reproducible measurements against it:

1. pnpm measure:bluesky — a read-only static compiler audit over all 1,660 authored JS/TS files using @hozo/migration-audit.
2. pnpm measure:bluesky:rnw-free — a production Expo Webpack build experiment that compiles app-owned .ts/.tsx through Hozo and blocks react-native and react-native-web module resolution to map the exact dependency boundary.

Both reports are committed in docs/measurements/ (bluesky-social-app.md and bluesky-rnw-free-build.md) so any change to compiler coverage or diagnostics shows up as a diff.

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Part 1: Static compiler audit (pnpm measure:bluesky)

Corpus scope

Metric	Value
Repository & commit	bluesky-social/social-app @ 007c893de107c2ecbf2188d618196075f19c8f5a
Authored files	1,660 (1,049 .tsx + 611 .ts, 7,216,111 bytes)
Platform split	1,550 shared · 89 .web · 21 .native / .ios / .android
Styling surface	651 files use style, 9 use className, 695 reference Bluesky’s atoms.*

Headline results

1. Zero parse or compile failures across all 1,660 files: extension-aware syntax selection parses .tsx as TSX and .ts as TypeScript (so generic arrow functions such as async <T>(...) => in .ts files parse cleanly without false TSX probe rejections).
2. 1,193 Web components and 1,149 Native components lowered across 573 files: with 0 UNLOWERED_REACT_NATIVE_JSX errors and 0 DOM style-array invariant violations ([styleA, styleB] passed raw to a DOM element).
3. The direct React Native JSX boundary on Web is closed: Web lowering retains 0 JSX tag occurrences bound to react-native across all 1,639 Web-eligible files. Every <View>, <Text>, <Pressable>, <ScrollView>, <FlatList>, <Image>, <TextInput>, <Modal>, <ActivityIndicator>, and <TouchableOpacity> in application JSX is lowered to semantic DOM or Hozo’s Web components.
4. 218 warnings, 0 errors:
   • 135 RN_COMPAT_NOT_INSTALLED (files where the Web compiler rewrote Platform, StyleSheet, Keyboard, or Dimensions imports to @hozo/rn-compat, which the unmodified Bluesky checkout does not have installed).
   • 60 MISSING_ACCESSIBILITY_LABEL and 17 PRESSABLE_NEEDS_ROLE (interactive elements or inputs in Bluesky’s source that have no accessible name or role).
   • 6 UNSUPPORTED_CLASS_ON_NATIVE (Web-specific class strings in the 9 files that use className).

What happens to react-native imports and values on Web

The audit’s binding-aware journals (reactNativeImportDecisions, reactNativeReferenceDecisions, and reactNativeValueDecisions) separate JSX tags from runtime value references:

• Imports (662 total react-native import specifiers in Web targets):
  • 212 moved to @hozo/rn-compat (StyleSheet, Platform, Keyboard, Dimensions, useWindowDimensions, AccessibilityInfo, PanResponder)
  • 28 moved to @hozo/core (Pressable, TextInput used as runtime values)
  • 129 type-only specifiers (StyleProp, ViewStyle, TextStyle, LayoutChangeEvent, etc.)
  • 293 retained on react-native (either JSX-only bindings whose tag uses were already lowered and removed, or platform services such as Linking, Share, AppState, InteractionManager, and LayoutAnimation)
• JSX tags (4,132 opening/closing tag occurrences in Web targets):
  • 4,117 lowered directly to HTML or Hozo Web runtime helpers
  • 15 preserved tag spellings whose import binding moved to @hozo/core or @hozo/rn-compat
  • 0 retained on react-native
• Reviewed member contracts (555 non-JSX runtime references in completed Web files):
  • 358 covered by reviewed @hozo/rn-compat member contracts (StyleSheet.create, StyleSheet.flatten, StyleSheet.hairlineWidth, StyleSheet.absoluteFill, Platform.OS, Platform.select, Keyboard.dismiss, Dimensions.get)
  • 66 retained with explicit migration guidance (Linking.openURL, Share.share, AppState.addEventListener, LayoutAnimation.configureNext, InteractionManager.runAfterInteractions)
  • 131 unreviewed / whole-value references (such as passing View or Animated into third-party HOCs like Animated.createAnimatedComponent)

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Part 2: Production Webpack RNW-free build experiment (pnpm measure:bluesky:rnw-free)

Closing the direct JSX boundary in source files is necessary, but it is not the same as building a production Web bundle without react-native-web. To measure the full dependency graph honestly, scripts/measure-rnw-free-build.mjs runs Bluesky’s production Expo Webpack build three ways:

1. Unmodified baseline: standard Expo Webpack production build.
2. Hozo-lowered build: app-owned src/**/*.{ts,tsx} runs through Hozo’s Web lowerer (unloweredReactNativeJsx: 'error') before Babel/Webpack.
3. Hozo-lowered + RNW blocked: the same Hozo-lowered build, but Webpack aliases react-native and react-native-web to an absent module so every remaining import request fails with an exact issuer trace.

What the three builds showed

Build	Webpack errors	Bundled react-native-web modules	What it proves
1. Unmodified baseline	0	74 modules (430,839 unminified bytes)	The baseline app builds cleanly and ships ~431 KB of react-native-web.
2. Hozo-lowered (src/)	0	71 modules	Hozo’s Web output compiles and bundles cleanly inside Bluesky’s production Webpack pipeline.
3. Hozo-lowered + RNW blocked	274 errors (270 requests from 177 modules)	0 modules	Removing react-native-web entirely is blocked by 35 app modules (non-JSX platform APIs) and 138 modules across 40 third-party packages.

Why 35 app modules and 40 third-party packages still requested react-native

1. Zero P0 Hozo core gaps in app code: after Hozo lowering and moving Pressable, TextInput, FlatList, ScrollView, and @hozo/rn-compat APIs, the P0 core-gap table (View, Pressable, FlatList, ScrollView, TextInput) and P1 foundation table (Dimensions, useWindowDimensions, useColorScheme, AccessibilityInfo) in reachable app modules are both 0.
2. The 35 app modules are platform services and imperative escape hatches: Linking, AppState, Share, InteractionManager, LayoutAnimation, Alert, BackHandler, findNodeHandle, and StatusBar. These are non-UI OS services rather than view/style primitives.
3. The 138 third-party modules come from 40 external React Native libraries: led by @sentry/react-native (24 modules), @react-navigation/elements (19), react-native-keyboard-controller (19), react-native-reanimated (9), @react-navigation/bottom-tabs (8), expo-image (5), react-native-progress (5), @react-navigation/native (4), and react-native-svg (4). Because those node_modules packages are published targeting react-native, fully eliminating react-native-web from a bundle that keeps those libraries requires either Web-specific package entry points or bundler-level aliasing to @hozo/rn-compat.

Reproducing both measurements locally

From a Hozo repository checkout:

sh

# 1. Static migration audit (~10s warm; clones pinned social-app into temp/social-app on first run)pnpm measure:bluesky# 2. Production Webpack RNW-free boundary experiment (requires Node 24 for Bluesky's lockfile)mise exec node@24.19.0 -- pnpm measure:bluesky:rnw-free