feat(spm): add trait to opt out of Firestore

[andrewheard]

Added support for configuring the Firebase Swift Package using Traits (SE-0450) and introduced a default-enabled Firestore trait.

Previously, adding the firebase-ios-sdk Swift package would always download and resolve Firestore's underlying dependencies (gRPC, abseil), even if the app didn't include Firestore. With package traits, you can now opt out of Firestore to reduce package resolution time, checkout size, and project overhead. The trait is enabled by default to preserve backwards compatibility.

Developer Instructions

Configuring Traits in Xcode (Xcode 26.4+)

1. In Xcode, select your project in the Project Navigator.

2. Select your project in the project editor and open the Package Dependencies tab.

3. In the package list, locate Firebase and find the Traits column.

4. Click the Traits dropdown (which shows default (Firestore) by default).

5. Uncheck default (or uncheck Firestore). The dropdown will display None when all traits are disabled.

Configuring Traits in Package.swift

In your Package.swift, pass an empty traits array (or list only the traits you wish to enable) in your .package dependency declaration:

// swift-tools-version: 6.1
import PackageDescription

let package = Package(
  name: "MyPackage",
  dependencies: [
    .package(
      url: "https://github.com/firebase/firebase-ios-sdk.git",
      from: "13.0.0",
      traits: [
        // Omit "Firestore" (or leave empty) to prune Firestore, gRPC, and Abseil dependencies.
      ]
    ),
  ],
  targets: [
    .target(
      name: "MyTarget",
      dependencies: [
        .product(name: "FirebaseAuth", package: "firebase-ios-sdk"),
      ]
    ),
  ]
)

---

Technical Details

Implementation

1. Package Trait Definition & Target Gating

• Trait declaration: Declared let firestoreTrait = Trait(name: "Firestore", ...) and enabled it by default in packageTraits via .default(enabledTraits: [firestoreTrait.name]).
• Target dependency conditions: Conditioned source and binary Firestore targets and their heavy third-party dependencies (abseil-cpp-binary, grpc-binary, FirebaseFirestoreInternalWrapper, abseil-cpp-SwiftPM, grpc-ios, and FirebaseFirestoreCombineSwift) on .when(traits: ["Firestore"]).

2. C Preprocessor Macro (FIRESTORE_TRAIT_ENABLED)

• SwiftPM traits pass -D <Trait> flags to swiftc for Swift conditional compilation, but do not automatically pass preprocessor defines to Clang for C/Objective-C compilation.
• Added cSettings: [.define("FIRESTORE_TRAIT_ENABLED", .when(traits: ["Firestore"]))] on FirebaseFirestoreTarget and objc-import-test so Clang can conditionally compile Firestore-related code based on the trait.

3. Compile-Time Diagnostic Guard

• In SwiftPM-PlatformExclude/FirebaseFirestoreWrap/dummy.m, added a #if !defined(FIRESTORE_TRAIT_ENABLED) #error check to provide an immediate, actionable diagnostic if an app target attempts to link FirebaseFirestoreTarget without enabling the Firestore trait.

4. Integration Tests & Conditional Imports

• In SwiftPMTests/swift-test/all-imports.swift, guarded import FirebaseFirestore behind #if Firestore // Gated by the "Firestore" SwiftPM package trait..
• In SwiftPMTests/objc-import-test/objc-header.m and objc-module.m, guarded imports behind #if defined(FIRESTORE_TRAIT_ENABLED).
• Verified that test targets build and pass both with default traits enabled and with --disable-default-traits.

5. CocoaPods & Combine Compatibility

• Preserved #if canImport(Combine) && swift(>=5.0) guards in FirebaseCombineSwift/Sources/Firestore source files to avoid breaking CocoaPods CI workflows (sdk.combine.yml), keeping trait gating at the target dependency level in Package.swift.

6. Integration Test App Opt-Out

• Configured FirebaseAI/Tests/TestApp/FirebaseAITestApp.xcodeproj/project.pbxproj to opt out of default package traits (traits = ()), validating trait opt-out in Xcode while avoiding unnecessary Firestore dependencies for AI Logic integration tests.

Testing

• Verified that swift test --test-product swift-test passed with default traits enabled.
• Verified that swift test --disable-default-traits --test-product swift-test passed with traits disabled.
• Verified that swift test --test-product objc-import-test passed with default traits enabled.
• Verified that swift test --disable-default-traits --test-product objc-import-test passed with traits disabled.
• Verified that compiling FirebaseFirestoreTarget with --disable-default-traits triggered the expected diagnostic in dummy.m.
• Verified in a standalone consumer app depending on FirebaseAuth with traits: [] that abseil-cpp-binary and grpc-binary were completely pruned and never downloaded during resolution.

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[gemini-code-assist]

Summary of Changes

This pull request introduces support for Swift Package Traits (SE-0450) to the Firebase iOS SDK, specifically targeting the Firestore module. By defining a default-enabled 'FirebaseFirestore' trait, the change allows developers to explicitly opt out of Firestore dependencies if they are not using the product, significantly streamlining the dependency graph for projects using only lightweight Firebase components. The implementation includes robust gating for source and binary targets, updated documentation, and diagnostic checks to ensure a smooth developer experience during configuration.

Highlights

• Swift Package Traits Integration: Implemented the FirebaseFirestore package trait in Package.swift, allowing developers to opt out of Firestore and its heavy dependencies (gRPC, abseil) to reduce package resolution overhead.
• Dependency Gating: Conditioned Firestore-related targets and binary dependencies on the presence of the FirebaseFirestore trait using SwiftPM's new conditional dependency syntax.
• Compile-time Diagnostics: Added a #error check in dummy.m to provide clear feedback if Firestore is linked while the trait is disabled.
• Test Suite Adaptability: Updated integration tests to conditionally import Firestore, ensuring test suites remain functional regardless of whether the trait is enabled or disabled.

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Activity

• Pull request created by andrewheard.
• Gemini Code Assist bot provided usage instructions.
• Author requested a summary via /gemini summary.

[gemini-code-assist]

Code Review

This pull request introduces support for Swift Package Traits (SE-0450) to allow developers to opt out of heavy dependencies like Cloud Firestore (gRPC and Abseil) when they are not needed. It configures the FirebaseFirestore trait in Package.swift and conditionally compiles dependencies and imports based on this trait. The review feedback highlights critical issues in the test files where conditional compilation checks were implemented incorrectly: in Swift, #if canImport(FirebaseFirestore) should be used instead of #if FirebaseFirestore, and in Objective-C, __has_include should be used instead of checking for undefined preprocessor macros, as they do not propagate transitively to the test targets.

[andrewheard]

Note: The CI failure is likely just due to #16690. Will re-run after merging.

[ncooke3]

Re-opening after #16544 merged.

[ncooke3]

Ah, my bad. Main needed to be merged in. I thought merging the other PR and restarting CI was enough. CI looks good now 👍 .