| name | spmforkmp |
| license | MIT |
| metadata | {"version":"1.1.1","last_updated":"2026-04-27T00:00:00.000Z"} |
| compatibility | Works with any Agent Skills compatible environment (Junie, Claude Code, Cursor, etc.). |
| description | Use this skill whenever working with the spmForKmp Gradle plugin (id: `io.github.frankois944.spmForKmp`) — a modern replacement for the deprecated Kotlin CocoaPods plugin for integrating Swift Package Manager (SPM) dependencies into Kotlin Multiplatform (KMP) projects targeting Apple platforms.
Trigger on any of these: configuring the spmForKmp plugin, adding Swift Package dependencies to a KMP project, writing Swift bridge code (`@objcMembers`) for Kotlin Multiplatform, migrating from `org.jetbrains.kotlin.native.cocoapods`, exporting Objective-C compatible packages to Kotlin (`exportToKotlin`), troubleshooting `Undefined symbol` or cinterop errors in KMP Apple targets, questions about `swiftPackageConfig {}`, Swift↔Kotlin interop, or anyone saying "spm4kmp", "spmForKmp", or "swift package" in a KMP/Kotlin Multiplatform context. Use this skill even if the user doesn't name the plugin explicitly — if they are trying to use a Swift library from Kotlin on an Apple platform, this skill applies.
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Definition of Done — Read This First
Any task that adds or removes a native dependency or product is NOT complete until the app launches successfully on a simulator (or device if no simulator is available) for each target platform configured in swiftPackageConfig — if the user has an Xcode project. This applies to migrations, new integrations, and any dependency change (add or remove). Gradle BUILD SUCCESSFUL is necessary but never sufficient.
Concretely, before reporting success you must have observed, in this order, for each Apple target platform declared in the KMP module (iOS, macOS, tvOS, watchOS — only those actually configured):
./gradlew :<app-module>:linkDebugFramework<Platform><Arch> succeeds — e.g. linkDebugFrameworkIosSimulatorArm64, linkDebugFrameworkMacosArm64, linkDebugFrameworkTvosSimulatorArm64, linkDebugFrameworkWatchosSimulatorArm64.xcodebuild … build against the app's .xcodeproj (or .xcworkspace if not CocoaPods-only) for the target platform succeeds.- Launch the app on a simulator for the platform (preferred):
- iOS / tvOS / watchOS:
xcrun simctl install <UDID> <path>.app then xcrun simctl launch <UDID> <bundle-id> — confirm a non-zero PID.
- macOS: run the
.app directly — confirm it opens without an immediate crash.
- Use a real device only when no simulator is available for that platform.
The full command sequence is in references/migration.md § "Final Verification — Build and Launch on a Simulator". If any step fails, treat the task as in-progress and continue debugging — do not declare success, do not summarize as "complete," do not stop until launch succeeds. If the user's environment genuinely cannot boot a simulator (e.g. CI without a Mac runner), say so explicitly and surface the unverified status — never silently elide the step.
What spmForKmp Does
spmForKmp compiles Swift code and SPM packages into a cinterop-based bridge that Kotlin can call on Apple targets. It handles:
- Bridge: Your Swift files in
src/swift/[bridgeName]/ are compiled and exposed to Kotlin via cinterop
- SPM Dependencies: External Swift packages fetched and linked into the bridge
- Export to Kotlin: ObjC-compatible packages exposed directly without a bridge wrapper
- Migration: Drop-in replacement for the
cocoapods {} DSL
How to Help the User
Before writing any Gradle snippet, fetch plugins.gradle.org/plugin/io.github.frankois944.spmForKmp to confirm the current plugin version and use that value in every code example. Never hard-code a version without verifying it first.
Identify the scenario, load the relevant reference file(s), then produce complete Gradle config + Swift code + Kotlin usage. Always produce the full picture — don't give only a dependency snippet without showing how the bridge and Kotlin usage fit together.
The Three Core Scenarios
Scenario A — Basic integration (no external SPM package)
The user only needs Apple SDK access (UIKit, Foundation, CoreLocation…) from Kotlin.
→ Load references/setup.md + references/bridge.md
Scenario B — Integration with an external SPM package
The user wants to add a third-party Swift package. Pick the dependency type that fits:
Always load references/setup.md and references/exporting.md for Scenario B. For every product the user adds, perform three checks before writing the Gradle config — never skip any of them:
- Min OS — look up the package's
.platforms declaration in its Package.swift and raise minIos/minMacos/minTvos/minWatchos if the new requirement is higher than the current value.
- ObjC compatibility — run the modulemap detection in
references/exporting.md and set exportToKotlin = true or false.
- Target type (binary vs. source) — open the dependency's
Package.swift and check whether the target backing the product is .binaryTarget(...) (XCFramework, often used by closed-source vendor SDKs like GoogleMaps, Firebase Crashlytics, etc.). If yes, add exportedPackageSettings { includeProduct = listOf("ProductName") } to the same swiftPackageConfig block and wire the auto-generated local Swift package into project.pbxproj. See rule 8 for the pbxproj edits. Skipping this check at config time produces a green Gradle build that fails Xcode link with Undefined symbol: _OBJC_CLASS_$_… — caught only by rule 9's platform launch, never by Gradle alone.
Scenario C — Migrate from the KMP CocoaPods plugin
→ Load references/migration.md. It contains the full before/after for Gradle, Xcode, and import statements.
Other references
Non-Negotiable Rules
Always apply these — they are the most common sources of user pain:
-
@objcMembers public class ... : NSObject is required. Any Swift class, method, or property that must be visible to Kotlin needs @objcMembers (or per-item @objc) and public. Pure Swift types (structs, enums, Swift-only protocols, actors, async/await) cannot cross the boundary.
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import io.github.frankois944.spmForKmp.swiftPackageConfig is required at the top of build.gradle.kts. Without this import the function resolves to a Gradle built-in with an incompatible signature and the build fails with "receiver type mismatch". Call it as target.swiftPackageConfig("bridgeName") { ... } — the bridge name is a positional string, not cinteropName =.
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Use the same bridge name across all Apple targets. Passing the same string to swiftPackageConfig on every target points them all to the same src/swift/[bridgeName]/ folder. Without a shared name each target gets its own directory.
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gradle.properties must contain kotlin.mpp.enableCInteropCommonization=true. Without it, the shared cinterop definitions will not resolve.
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Kotlin 2.x requires opting into ExperimentalForeignApi at cinterop call sites. The cleanest way is one line per target in Gradle: target.compilerOptions.optIn.add("kotlinx.cinterop.ExperimentalForeignApi"). Alternatively annotate individual Kotlin files with @OptIn(kotlinx.cinterop.ExperimentalForeignApi::class).
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Every time a dependency or product is added, re-check the minimum OS version and update the plugin config. Read the new package's .platforms in its Package.swift and raise minIos/minMacos/minTvos/minWatchos if the new requirement exceeds the current value. The configured minimum must always reflect the highest requirement across all dependencies in the block — each new addition may raise the bar. Never skip this step: a mismatch causes a build error. If the package has no .platforms block, no change is needed.
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Always set exportToKotlin explicitly — never omit it. For each product, run the detection steps in references/exporting.md § "Detecting ObjC Compatibility via the Modulemap" and set exportToKotlin = true only when the check confirms ObjC compatibility on the direct target backing the product. Transitive dependencies do not count — cinterop only sees the direct target's interface. If the check cannot be performed (inaccessible source, closed-source binary), set exportToKotlin = false. When in doubt, false is always the safe default.
-
Some dependencies must be added to Xcode as a local package — the plugin tells you which ones. After each Gradle build, the plugin evaluates every dependency using three criteria and generates a local Swift package for those that need Xcode-side linking:
- Always included: C/ObjC modules (
isCLang) are unconditionally added.
- Explicitly included: any product listed in
exportedPackageSettings { includeProduct = listOf("ProductName") }.
- Auto-detected: the plugin scans compiled output dirs for static
.framework files (reads Info.plist, calls isDynamicLibrary) and includes any static framework it finds. Detection is not 100% reliable — binary XCFrameworks in particular may be missed.
When the local package is generated and hideLocalPackageMessage is false, the plugin prints a logger.error message (always visible, even without --info):
Spm4Kmp: The following dependencies [ProductName] need to be added to your xcode project
A local Swift package has been generated at <module>/exported<BridgeName>
Please add it to your xcode project as a local package dependency
Add that generated package to your Xcode project as a local package dependency (File → Add Package Dependencies → Add Local… in Xcode). Once added, set spmforkmp.hideLocalPackageMessage=true in gradle.properties to silence the message.
If a dependency is NOT auto-detected and causes Undefined symbol at Xcode link time, add it explicitly: exportedPackageSettings { includeProduct = listOf("ProductName") } in the same swiftPackageConfig block, then rebuild.
Always run xcodebuild -resolvePackageDependencies -project … | tail -n 50 before xcodebuild … build | tail -n 50 after adding the local package. Building without resolving first fails with Missing package product even when the project is correctly configured.
For manual project.pbxproj editing (CI or no Xcode UI), see references/troubleshooting.md § "Undefined symbol".
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A task is not complete until the app launches successfully on each configured Apple target platform. This is the definition of done for every spmForKmp task — see the "Definition of Done" section at the top of this file. Gradle success only proves the bridge compiles; the Xcode build proves linking and embedding; the launch proves the framework loads at runtime with no missing symbols. Run the full sequence in references/migration.md § "Final Verification" — xcodebuild build against the .xcodeproj (or the .xcworkspace if it's not CocoaPods-only) for each declared platform, then launch on a simulator (iOS/tvOS/watchOS) or run directly (macOS). If any step fails or you cannot run the target, do not report success — keep debugging or surface the unverified status explicitly.
The bridge folder also needs at least one .swift file even when exportToKotlin = true for every product. Swift PM rejects an "empty" target with target '<bridgeName>' referenced in product '<bridgeName>' is empty, so a .gitkeep is not enough — drop in a one-line Bridge.swift containing import Foundation.
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Only generate Swift bridge code if the user explicitly asks for it. Do not produce src/swift/[bridgeName]/*.swift content unless the user requests it — show the Gradle config and Kotlin usage only. When the bridge file is needed (pure Swift dependency that cannot be called directly), state that a bridge is required and ask the user what functionality they want exposed before writing any Swift.
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Adding or removing any native dependency or product requires a launch on each configured target platform — if the user has an Xcode project. Every add or remove changes the linked binary surface: new symbols must resolve at runtime, removed symbols must not leave dangling references. For each platform present in swiftPackageConfig (minIos, minMacos, minTvos, minWatchos), run the app on a simulator first (xcrun simctl launch <UDID> <bundle-id>) and confirm a non-zero PID with no immediate crash. Use a real device only when no simulator is available for that platform (e.g. watchOS on older Xcode versions). If the user has no Xcode project (library-only, no app target), state that the launch step is skipped and why — never silently omit it.
