How to debug hermec failure in RN release build process?

[liamjones]

I'm currently trying to switch our RN 0.74.6 apps over from the JSC to Hermes.

Enabling it seems to work fine with the packager but I'm not able to get hermesc -emit-binary to produce the .hbc file during the bundle process. The process runs, exits with code 0 but doesn't write a file. I've tried playing with some of the command line options to get some debug output but I'm not having much luck so far.

Can anyone give me some pointers on where to look/some options to set to work out what's going on?

I've tried it with an empty RN 0.74.6 app from the template, and that produces the .hbc fine so I guess it's something to do with our JS but it's strange than hermesc is exiting with a 0 exit code.

[tmikov]

Hi, when you manually invoke Hermes from the terminal, does it still fail to produce a fail? What are the exact command line options you are using?

[liamjones]

Hi @tmikov, yes it was still exiting with a 0 code but produced no file. The command I was running was extracted from the RN Gradle plugin by debugging ./gradlew :app:createBundleReleaseJsAndAssets task:

../../../node_modules/react-native/sdks/hermesc/osx-bin/hermesc -emit-binary -max-diagnostic-width=80 -out /Users/liam.jones/code/iris/packages/apps/lw-app/android/app/build/generated/assets/createBundleReleaseJsAndAssets/index.android.bundle.hbc /Users/liam.jones/code/iris/packages/apps/lw-app/android/app/build/generated/assets/createBundleReleaseJsAndAssets/index.android.bundle -O -output-source-map

Weirdly, I just reran it, and I'm now getting the .hbc output file, but I'm not sure what's changed.

I don't think I was putting the output in the wrong directory and missing that the file was created because I originally investigated this when Sentry complained it couldn't find the .hbc (or .hbc.map?) for upload of debug info from Hermes. 🤔

Apologies for wasting your time, I'll come back to this thread if I see it happen again.