iOS fails to run on apps generated using 12.5.0

[joemckie]

There is an issue with the latest version of this package (which is using a release candidate version of react-native) which causes run-ios to fail with the following error:

/Users/xxx/www/sandbox/nx-react-native-test/node_modules/metro-hermes-compiler/src/emhermesc.js:77
          throw ex;
          ^

RuntimeError: abort(TypeError: Cannot read property 'toUpperCase' of undefined). Build with -s ASSERTIONS=1 for more info.
    at process.abort (/Users/xxx/www/sandbox/nx-react-native-test/node_modules/metro-hermes-compiler/src/emhermesc.js:440:13)
    at process.emit (events.js:375:28)
    at processPromiseRejections (internal/process/promises.js:245:33)
    at processTicksAndRejections (internal/process/task_queues.js:96:32)

I managed to fix this by installing the previous version (12.3.6) and generating the app using that. Bumping the version up to 12.5.0 afterwards causes no issues.

I'm not entirely sure what is causing this issue (although I imagine it might be the version of react-native), but thought I'd raise this issue and offer a solution as it was a struggle getting this to work out of the box.

[joemckie]

TLDR for people looking for a quick fix: Generate your app using 12.3.6. You can bump the version afterwards if you like.

[xiongemi]

are you using yarn?
you might need to add in package.json:

"resolutions": {
    "metro": "0.66.0"
  }

basically, @react-native-community/cli has dependency of metro “^0.66.0”, which installs 0.66.1