[chrfalch]

Summary:

When a library has no Package.swift, SwiftPM autolinking stops the build with an error. If the library mixes Swift and Objective-C, the error says to opt the library out. Otherwise, it says to run npx react-native spm scaffold.

To decide, the check scanned every file in the library on disk. A Swift file that the podspec never compiles still counted. Example: @react-native-google-signin/google-signin compiles only ios/**/*.{h,m,mm}, but it also ships expo/ios/ExpoAdapterGoogleSignIn/GoogleSignInAppDelegate.swift. So the build told users to opt out an Objective-C library that spm scaffold can handle.

The scaffolder already decides from the files the podspec compiles. This change makes the autolinker use the same rule:

1. The autolinker reads the podspec the scaffolder would read: the podspecPath from the autolinking config, else the first podspec in the package root.
2. It expands source_files from the package root and removes exclude_files, using the same code as the scaffolder (moved into a shared podspecSourceFiles helper).
3. It decides "mixed" with the same predicate as the scaffolder (shared isMixedLanguageSourceList).
4. If there is no podspec, or the podspec cannot be read, it falls back to the disk scan as before.
5. The podspec is read only on this error path, so normal builds do not change.
6. spm.modules (app-local code, no podspec) keep the disk scan.

Changelog:

[IOS] [FIXED] - SwiftPM autolinking no longer reports a library as mixed Swift/Objective-C because of Swift files its podspec does not compile

Test Plan:

New tests in generate-spm-autolinking-test.js: a library with an Objective-C podspec and a stray Swift file (must say "run spm scaffold"), a podspec that compiles Swift and Objective-C (must say mixed), exclude_files removing the only Swift file, a configured podspecPath next to another podspec, a podspec in ios/ with a nested sourceDir, and unit tests for the predicate. These failed before the change.

yarn jest packages/react-native/scripts/spm
# Test Suites: 25 passed, 25 total
# Tests:       1205 passed, 1205 total

yarn eslint --max-warnings 0 packages/react-native/scripts/spm
# no warnings

Not run locally: yarn flow-check. My local Flow version did not match the repo's required version, so I rely on CI for Flow.