Extend Swift file updater to support xcode swiftpm dependency update

[AbhishekBhaskar]

What are you trying to accomplish?

This PR adds support for updating Package.resolved files in Xcode-managed SwiftPM projects that don't have a Package.swift manifest, enabling Dependabot to generate dependency update PRs for .xcodeproj-only Swift projects.

Changes:
New file: swift/lib/dependabot/swift/file_updater/xcode_lockfile_updater.rb

• Updates Package.resolved files in-place without running Swift CLI
• Preserves original schema version (v1/v2/v3) format
• Matches dependencies by identity or normalized URL
• Only updates resolved files relevant to each dependency (based on .xcodeproj directory)

Modified: file_updater.rb

• Added xcode_spm_mode? detection when experiment is enabled and no Package.swift exists
• Added updated_xcode_spm_files method for Xcode-managed updates
• Updated check_required_files to accept Xcode Package.resolved files

Modified:[update_checker.rb

• Handle nil preferred_resolvable_version for revision-only or branch-pinned dependencies

Modified: metadata_finder.rb

• Handle "default" source type by inferring source from dependency name

Anything you want to highlight for special attention from reviewers?

Behaviour:

• Behind enable_swift_xcode_spm experiment flag
• Updates correct Package.resolved files with minimal changes
• Supports multiple Xcode projects in single repo
• Produces clean JSON diffs matching Xcode's formatting

How will you know you've accomplished your goal?

Checklist

• I have run the complete test suite to ensure all tests and linters pass.
• I have thoroughly tested my code changes to ensure they work as expected, including adding additional tests for new functionality.
• I have written clear and descriptive commit messages.
• I have provided a detailed description of the changes in the pull request, including the problem it addresses, how it fixes the problem, and any relevant details about the implementation.
• I have ensured that the code is well-documented and easy to understand.

[Copilot]

Pull request overview

Adds experimental support in the Swift ecosystem for updating Xcode-managed SwiftPM projects that only contain .xcodeproj files (no Package.swift) by editing Xcode Package.resolved files in-place, enabling Dependabot PRs for these repos.

Changes:

• Introduces an Xcode-specific Package.resolved updater that preserves schema versions (v1/v2/v3) and formatting.
• Adds xcode_spm_mode? branching in the Swift FileUpdater to update Xcode lockfiles without invoking the Swift CLI.
• Improves Swift UpdateChecker and MetadataFinder handling for revision/branch pins and dependencies without explicit source type.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
swift/spec/dependabot/swift/file_updater_spec.rb	Adds integration coverage for Xcode SPM mode updating the correct Package.resolved file(s).
swift/spec/dependabot/swift/file_updater/xcode_lockfile_updater_spec.rb	Adds unit tests for updating v1/v2/v3 resolved schemas and error cases.
swift/lib/dependabot/swift/update_checker.rb	Avoids T.must on nil preferred_resolvable_version for revision/branch-pinned deps.
swift/lib/dependabot/swift/metadata_finder.rb	Infers source from dependency name when source_type is default/nil.
swift/lib/dependabot/swift/file_updater/xcode_lockfile_updater.rb	Implements in-place JSON update logic for Xcode Package.resolved.
swift/lib/dependabot/swift/file_updater.rb	Adds experiment-gated Xcode mode and updates required-files logic accordingly.

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