Source code is not preserved in EAS development builds when 'show source' is used with Hermes

[andrey-abstracted]

Build/Submit details page URL

https://expo.dev/accounts/duxa/projects/test-app/builds/e026acc3-9e93-492b-921b-4eaca532e769

Summary

In EAS development builds .toString() returns byte code for functions where 'show source' directive is used which should be preserving source code with Hermes. Works correctly in EAS production builds.

This is the description of the directive
facebook/hermes#114 (comment)

It is possible that the Metro bundler strips the bundle of the directive

Managed or bare?

eas build

Environment

expo-env-info 1.0.5 environment info:
System:
OS: macOS 13.5
Shell: 5.9 - /bin/zsh
Binaries:
Node: 18.16.0 - /usr/local/bin/node
Yarn: 1.22.19 - /usr/local/bin/yarn
npm: 9.8.1 - /usr/local/bin/npm
Watchman: 2023.06.26.00 - /usr/local/bin/watchman
Managers:
CocoaPods: 1.11.2 - /usr/local/bin/pod
SDKs:
iOS SDK:
Platforms: DriverKit 22.4, iOS 16.4, macOS 13.3, tvOS 16.4, watchOS 9.4
IDEs:
Android Studio: 2020.3 AI-203.7717.56.2031.7583922
Xcode: 14.3.1/14E300c - /usr/bin/xcodebuild
npmPackages:
expo: ~49.0.8 => 49.0.8
react: 18.2.0 => 18.2.0
react-native: 0.72.4 => 0.72.4
npmGlobalPackages:
eas-cli: 5.0.2
Expo Workflow: managed

Error output

showMySource.toString() prints out the following:
function showMySource() { [bytecode] }

Reproducible demo or steps to reproduce from a blank project

import { StatusBar } from 'expo-status-bar';
import { StyleSheet, Text, View } from 'react-native';

export default function App() {

function showMySource(){
'show source';
var a = 3;
var b = 4;
var c = a+b;
}

return (
<View style={styles.container}>
<Text>{showMySource.toString()}</Text>
<StatusBar style="auto" />
</View>
);
}

const styles = StyleSheet.create({
container: {
flex: 1,
backgroundColor: '#fff',
alignItems: 'center',
justifyContent: 'center',
},
});

[AlanSl]

Edit: my specific similar issue below (it not working on first load only) seems to be a known issue on Hermes: 'show source' does not work on first run when debugging, see also Hermes "show source" not working in debug mode. which is similar but not resolved in hot reloads.

---

I see the same issue (Expo 50.0.7 and 49.0.15), but curiously, only in the initial load, not on "hot reload" after making and saving an incidental change. There's another similar report over on the original issue on Hermes, that is also specific to Expo and mentions it being only on initial dev build load, and not hot reload.

Given something like this:

function someFunction () {
  'show source'
  return 'hello'
}
console.log(someFunction.toString())

• If I start an Expo app that already contains this, the 'show source' is ignored and it just shows [byteCode]:
  
• If I make a change and save the file (triggering hot reload), suddenly the 'show source' works as expected:
  
• If I then cause a reload (e.g. press r in the console), then it goes back to the failing case showing [byteCode]:
  

If "Fast Refresh" is disabled in the Expo Dev menu, it always shows the [byteCode] fail case; if I re-enable it, it does a hot reload that causes the full function code to show, and reverts to the above behaviour.