[andrewheard]

Xcode 26.2 doesn't enable a package's default traits when an Xcode project (.xcodeproj) adds the package by its URL. As a result, every .when(traits: ["Firestore"]) condition in Package.swift evaluates to false for these apps, even though they never turned the trait off:

• FirebaseFirestore and its dependencies (gRPC, Abseil) aren't linked.
• FIRESTORE_TRAIT_ENABLED isn't defined, so the build fails with the #error in SwiftPM-PlatformExclude/FirebaseFirestoreWrap/dummy.m: "FirebaseFirestore was included in your project dependencies, but the 'Firestore' SwiftPM package trait is disabled…"

Xcode 26.2 also has no Traits UI (it was added in Xcode 26.4), so affected developers have no workaround. Packages that depend on Firebase in their own Package.swift, local package references, and Xcode 26.4+ are not affected.

Fix

Since we can't require Xcode 26.4 yet, Package.swift now ignores the Firestore trait on Swift 6.2 (the Swift version in Xcode 26.2):

• Added isFirestoreTraitConditionSupported, gated by #if compiler(>=6.3). A manifest can't check the Xcode version, so the Swift compiler version stands in for it.
• Added two helpers, firestoreTraitDependencyCondition(platforms:) and firestoreTraitBuildSettingCondition(), and routed all 15 .when(traits: ["Firestore"]) call sites through them (binary and source Firestore). On Swift 6.2 they drop the trait requirement, so Firestore is always linked and FIRESTORE_TRAIT_ENABLED is always defined. On Swift 6.3+ they return the same conditions as before.
• The Firestore trait is still declared on Swift 6.2. SwiftPM 6.2 fails to resolve any dependent that passes traits: (even traits: []) to a package that declares no traits, so removing the declaration would break existing opt-outs.
• Added a firestoreTraitName string constant. In Swift 6 language mode, the helper functions can't read the non-Sendable firestoreTrait global.
• Expanded the trait documentation: how to opt out in Package.swift and in Xcode, removing the FirebaseFirestore product afterward, and the Xcode 26.2 limitation.
• Added a Firestore/CHANGELOG.md entry.

Trade-off

On Swift 6.2, opting out of the Firestore trait has no effect, including for swift build users. Opting out requires Xcode 26.4 / Swift 6.3 or later. The workaround can be removed once Firebase requires Xcode 26.4.

Testing

Reproduced the bug with a minimal package that declares a default-enabled trait and uses it in a cSettings define, a Swift #if check, and a target dependency. Before the fix, the trait was enabled in every case except one:

Consumer	Xcode	Trait enabled?
swift build (root package)	26.2	✅
xcodebuild (root package)	26.2	✅
Package dependency, by path and by URL (swift build and xcodebuild)	26.2	✅
.xcodeproj, local package reference	26.2	✅
.xcodeproj, remote package reference	26.2	❌
.xcodeproj, remote package reference	26.4	✅

After applying the same pattern to the reproduction, the .xcodeproj remote package reference on Xcode 26.2 builds, gets -DFIRESTORE_TRAIT_ENABLED, and builds the trait-conditioned dependency.

Also verified:

• swift package dump-package succeeds with both Xcode 26.2 and 26.4, with and without FIREBASE_SOURCE_FIRESTORE. On 26.2 there are no trait conditions; on 26.4 all trait conditions are unchanged.
• On Swift 6.2, a dependent passing traits: [] still resolves.

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