Add SPM support for Apple Embedded plugins (.gdip)

[gumaciel]

Add spm_packages key to the [dependencies] section of .gdip files, allowing plugins to declare Swift Package Manager dependencies with exact version pinning. The export pipeline generates the corresponding PBX entries in the Xcode project.

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Satisfies godotengine/godot-proposals#4758. Thanks to @MileyHollenberg for initial integration with Cocoapods and telling us about SPM!

Docs PR: godotengine/godot-docs#11805

This PR prevents external plugins from having to rely on hacky workarounds (like post-export scripts) to add Swift Package Manager (SPM) dependencies.

SPM is an excellent addition that will massively simplify the distribution and usage of iOS plugins because:

• No more post-export hacks: Plugins no longer need complex export scripts to manipulate the generated Xcode project.
• One-Click Deploy: SPM dependencies are natively resolved, guaranteeing that One-Click Deploy works out of the box.
• CI/CD Ready: Natively supports automated build pipelines.
• Lighter, Cleaner Plugins: Plugins become significantly smaller and simpler since heavy frameworks no longer need to be downloaded or embedded in the repository.

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This implementation was designed with developer experience in mind. The new .gdip format places the SPM packages directly inside the existing [dependencies] section:

[dependencies]
linked=[]
embedded=[]
system=["AppTrackingTransparency.framework"]
capabilities=[]
files=[]
linker_flags=["-ObjC"]
spm_packages=[
  {
    "url": "https://github.com/googleads/swift-package-manager-google-mobile-ads.git",
    "version": "12.14.0",
    "products": ["GoogleMobileAds"]
  }
]

This approach is highly beneficial because:

1. Self-Documenting: The JSON-like Array[Dictionary] format exposes url, version, and products explicitly.
2. Extensible: More keys (like platforms or checksums) can be easily added in the future without breaking the parser.
3. Familiarity: It respects and closely follows how SPM natively structures its package dependencies.
4. Deterministic Builds: The export pipeline forces the Xcode requirement kind to be exactVersion. This guarantees reproducible builds and prevents bugs caused by dependencies silently updating to different versions.
5. 100% Backwards Compatible: Older Godot versions parsing this .gdip file will simply ignore the spm_packages key safely.

Data Flow Diagram:

flowchart TD
    A["📄 .gdip file<br/><b>[dependencies]</b><br/>spm_packages=[...]"] -->|ConfigFile::load| B["load_plugin_config()<br/><i>plugin_config_apple_embedded.cpp</i>"]
    B -->|"Vector&lt;SPMPackage&gt;"| C["_export_apple_embedded_plugins()<br/><i>editor_export_platform_apple_embedded.cpp</i>"]
    C -->|Deduplicate by URL| D["PBX Generation"]
    D --> E["spm_packages<br/><i>packageReferences list</i>"]
    D --> F["spm_package_refs<br/><i>XCRemoteSwiftPackageReference</i>"]
    D --> G["spm_package_products<br/><i>XCSwiftPackageProductDependency</i>"]
    D --> H["modules_buildfile<br/><i>PBXBuildFile</i>"]
    D --> I["modules_buildphase<br/><i>Frameworks build phase</i>"]
    E --> J["_fix_config_file()<br/>Template Substitution"]
    F --> J
    G --> J
    H --> J
    I --> J
    J -->|"$spm_packages<br/>$spm_package_refs<br/>$spm_package_products"| K["📦 project.pbxproj<br/><i>Xcode resolves SPM at build time</i>"]

Loading

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Binaries: poing-godot-admob-ios.zip

Follow plugin tutorial if needed (just don't follow the Cocoapods step, this should be automatically now with SPM): https://www.youtube.com/watch?v=TB7WhP8mieo

Or:

• Clone repository: https://github.com/poingstudios/godot-admob-plugin
• Checkout to branch 205-prepare-for-spm-godot-47
• Download the poing-godot-admob-ios.zip
• Paste into res://ios/plugins
• Export the project

[gumaciel]

[stuartcarnie]

Looks great – just one nit.

[stuartcarnie]

@gumaciel you will need to rebase on the master branch and squash your commits too

[gumaciel]

@stuartcarnie I've done the rebase + squash commits, please check again if possible

Just a question: Previously, I've done a merge commit with the master branch. Is this not allowed in PRs?