Add regression tests for the iOS SwiftPM tooling

[chrfalch]

Summary:

Recent fixes to the iOS SwiftPM tooling (scripts/spm) all fixed bugs that CI did not catch. Adopters found them first. Each fix added a test for its own bug only. The bugs fall into a few classes: output that changes when nothing changed, generated names that collide or do not resolve, values that are hard-coded instead of read from the app, machine-specific paths in files that users commit, and malformed files that Xcode tolerates.

This PR adds two test-only tools that look for each class in general. They run in the existing Linux Jest job (test_js). No production code changes.

1. Invariant checker (spm-invariants.js, not a test file itself). It reads the files that the tooling generates and returns a list of violations:

   • no machine paths (temp dir, $HOME, absolute build-setting values) in project.pbxproj, .xcscheme, or .spm-injected.json;
   • the scheme parses as XML, and the pre-action script keeps its line breaks;
   • in every generated Package.swift, target and product names are unique (also case-insensitive) and valid C99 identifiers, and every dependency resolves, including products of local .package(path:) dependencies;
   • every generated or scaffolded manifest uses the app's iOS deployment target; the codegen manifest, whose template fixes .iOS(.v15), must not be above it;
   • project.pbxproj is balanced, every referenced object ID is defined, and the frameworks in .spm-injected.json match the project.

   Each rule also fails when the file or field it checks is missing, so a check cannot pass by finding nothing.

2. Lifecycle test (spm-lifecycle-test.js + spm-fixture-app.js). It builds a fake app on disk (deployment target 16.4), fake prebuilt artifacts for two React Native versions, and four fake libraries: one with its own Package.swift, one podspec-only library with module_name different from its npm name, one scoped @acme/… package, and one autolinking plugin with a flavored framework. It then runs scaffold → add → sync → sync → update (same version) → update (next version) → deinit through setup-apple-spm.js, and runs the checker after each step. It also asserts:

   • a second sync changes no byte and replaces no libs/ entry;
   • the build-time stale check reacts to the right changes and ignores files that Xcode writes;
   • a plugin framework mismatch makes sync exit with code 2;
   • update to the same version and deinit restore the project and scheme byte for byte.

   Network access, plutil, otool, codegen and pod are mocked, so the test runs offline on Linux.

Changelog:

[INTERNAL] [ADDED] - Add regression tests for the iOS SwiftPM tooling

Test Plan:

yarn jest --no-cache -i packages/react-native/scripts/spm/__tests__

Result: 24 suites, 1124 tests, all passed, about 23 s (on main at dd9b6c5). The two new suites take about 4 s.

Each earlier fix was undone one at a time with git show <sha> -- ':!**/__tests__/**' | git apply -R, and the new tests failed each time:

Fix reverted	New tests failing
#58826 (scheme pre-action newlines)	9
#58292 (absolute HERMES_CLI_PATH in pbxproj)	9
#58597 (libs/ rewritten on every sync)	2
#58828 (watched path absent at add time)	1

yarn eslint and prettier --check on the new files: clean.

Not run: Linux locally. The test_js job on this PR is the first Linux run.

[cipolleschi]

Thanks. foradding some tests

[meta-codesync]

@cipolleschi has imported this pull request. If you are a Meta employee, you can view this in D126304581.