feat: improve monorepo support by removing redundant PROJECT_ROOT

[grabbou]

Summary

Historically, React Native didn't support a lot of custom project structures apart from the standard flat directory with ios and android folders. The CLI had to be explicitly started from the project root, otherwise Metro didn't work right.

In order to resolve the project root in the most accurate way, React Native assumed that project root is always ../../ from its location in node_modules - this is not true when the installation gets hoisted (e.g. in a monorepo).

To address that, @janicduplessis brought support for custom PROJECT_ROOT that allowed overriding the ../../ in case it wasn't true.

Today, CLI is able to automatically resolve the project root, no matter where it's started. It will traverse the tree of the directories upwards and stop as soon as it meets package.json.

As a result, it doesn't really matter from where we start the CLI anymore as a part of react-native-xcode.sh.

By replacing the default value of $REACT_NATIVE_DIR/../../ with $PWD, that is default for all Xcode scripts, we can make the setup for monorepo easier - nobody will need to set $PROJECT_ROOT` in order to override the incorrect defaults.

By default, all scripts defined in Xcode run from $PWD directory, which is the location of the iOS project. In the future, we will be able to remove cd entirely.

To better understand this PR, let's look a few hypothetical structures as an example:

Monorepo:

tl;dr works out of the box, no need to mess around with paths

- package.json
- packages/
  - my-app/
     - index.js
     - package.json
     - ios/
        - MyApp.xcodeproj

Before this PR, the react-native-xcode.sh will start the CLI like this:

cd $REACT_NATIVE_DIR/../../
node <absolute_path_to_cli.js> bundle --entry-point index.js

• Because we change the directory to the root of monorepo, CLI throws an error. All in all, there's no react-native dependency at the workspace root.

• Some users turn no hoist in an act of troubleshooting the errors, which resolves the problem - react-native is moved under my-app/node_modules which makes this mechanism resolve properly.

• Some users find out about PROJECT_ROOT and set it to overwrite the default value. For example, setting export PROJECT_ROOT = "$PWD/../ will set the directory to my-app, which has a dependency on react-native in a package.json and makes the CLI happy.

After this PR, the react-native-xcode.sh will start the CLI like this:

cd $PWD
node <absolute_path_to_cli.js> bundle --entry-point index.js

• The $PWD is packages/my-app/ios/ because that's where the Xcode project is located. CLI will automatically set the root to ../ because that's where it finds package.json with react-native dependency. It will pass that root to Metro, unless users have set a different one themselves. Thanks to that, all paths to JavaScript files remain working and unaffected.

• No need to set PROJECT_ROOT anymore.

• We don't rely on the location of node_modules, which is cleaner and future proof.

Standard:

tl;dr no changes

- ios/
   - MyApp.xcodeproj
- index.js
- package.json

Before this PR, the react-native-xcode.sh will start the CLI like this:

cd $REACT_NATIVE_DIR/../../
node <absolute_path_to_cli.js> bundle --entry-point index.js

• Everything works fine. Path from react-native inside node_modules is correct - the project root is set right to /

After this PR, the react-native-xcode.sh will start the CLI like this:

cd $PWD
node <absolute_path_to_cli.js> bundle --entry-point index.js

• The root will be set to where Xcode project is located, which is /ios. This is the PWD for all Xcode scripts.

CLI will look for the package.json going upwards from ios folder. Will stop at /, find out it has react-native dependency, load it and its commands and proceed further.

Changelog

[iOS] [Feature] - Better monorepo support when building release apk

Test Plan

• All projects (standard/monorepo) run without issues.
• PROJECT_ROOT is not needed.

CC: @Titozzz (who wrote monorepo guide), @alloy, @bartolkaruza

[grabbou]

I would remove this entirely, but I don't really want to run into all the users that have some crazy setup today. Historically, there was a lot of hacks around setting up monorepos and we're working with the CLI team to educate the developers that some of these are not needed anymore.

[Titozzz]

Cool changes, less user pain is great

[alloy]

Nice one 👌

[facebook-github-bot]

@hramos has imported this pull request. If you are a Facebook employee, you can view this diff on Phabricator.

[react-native-bot]

This pull request was successfully merged by @grabbou in a8e8502.

^{When will my fix make it into a release? | Upcoming Releases}

[stigi]

I know this PR is old, but I believe we have a bug here. If $PWD is going to be the ios folder when this script is invoked from Xcode, then this line should be

PROJECT_ROOT=${PROJECT_ROOT:-$PWD/..}

cc @grabbou

[kelset]

@stigi would you mind opening a PR agains the main repo with the one line change you propose there? Once it's up it'd be way easier to test it & then have the fix you are proposing available for everyone :)

[stigi]

@kelset I was to quick to shoot. There's already a PR that is discussing the issue. It's not only PROJECT_ROOT that's broken, but also REACT_NATIVE_DIR. I left my comments in the PR #29477 (comment)

[KingAmo]

is there a guide on how to use monorepo with this pr ?