Add contribution hint extensions for cross module compilation

README.md

@@ -17,9 +17,9 @@ rewrite our code generation setup to use Metro.
 Please note that we are sharing this repository strictly as a practical demonstration of code generation with Metro. 
 This is a reference example and is not intended for public adoption.
 
-> **⚠️ Metro's extensions API is highly experimental and does not accept any FRs and issues. The Kotlin compiler plugin 
-> API itself is also constantly changing and lacks documentation. You should be aware of the high-maintenance cost if
-> you decide to follow the same approach.**
+> **⚠️ [Metro's extensions API](https://github.com/ZacSweers/metro/blob/main/compiler/API.md) is highly experimental 
+> and does not accept any FRs and issues. The Kotlin compiler plugin API itself is also constantly changing and lacks
+> documentation. You should be aware of the high-maintenance cost if you decide to follow the same approach.**
 
 ## Performance Benchmark
 

compiler-plugin/resources/META-INF/services/dev.zacsweers.metro.compiler.api.fir.MetroContributionHintExtension$Factory

@@ -0,0 +1,3 @@
+com.bandlab.metro.station.graph.MetroStationHintExtension$Factory
+com.bandlab.metro.station.entry.StationEntryHintExtension$Factory
+com.bandlab.metro.station.configselector.ContributesConfigSelectorHintExtension$Factory

compiler-plugin/src/com/bandlab/metro/station/MetroStationPluginComponentRegistrar.kt

@@ -25,7 +25,7 @@ public class MetroStationPluginComponentRegistrar : CompilerPluginRegistrar() {
     override val supportsK2: Boolean get() = true
 
     override fun ExtensionStorage.registerExtensions(configuration: CompilerConfiguration) {
-        val stationEntriesBaseline = configuration.get(MetroStationConfigurationKeys.STATION_ENTRIES_BASELINE)
+        val stationEntriesBaseline = configuration[MetroStationConfigurationKeys.STATION_ENTRIES_BASELINE]
         FirExtensionRegistrarAdapter.registerExtension(
             MetroStationPluginRegistrar(
                 includeBaselineChecker = stationEntriesBaseline != null,

compiler-plugin/src/com/bandlab/metro/station/configselector/ContributesConfigSelectorHintExtension.kt

@@ -0,0 +1,52 @@
+package com.bandlab.metro.station.configselector
+
+import com.bandlab.metro.station.utils.ClassIds
+import dev.zacsweers.metro.compiler.MetroOptions
+import dev.zacsweers.metro.compiler.api.fir.MetroContributionHintExtension
+import dev.zacsweers.metro.compiler.api.fir.MetroContributionHintExtension.ContributionHint
+import dev.zacsweers.metro.compiler.compat.CompatContext
+import org.jetbrains.kotlin.fir.FirSession
+import org.jetbrains.kotlin.fir.extensions.FirDeclarationPredicateRegistrar
+import org.jetbrains.kotlin.fir.extensions.predicateBasedProvider
+import org.jetbrains.kotlin.fir.symbols.impl.FirRegularClassSymbol
+
+/**
+ * Implements [MetroContributionHintExtension] to generate cross-module contribution hint files
+ * for `MultibindingContribution` interfaces generated by [ContributesConfigSelectorFir].
+ *
+ * These hint files allow Metro's `ContributionHintFirGenerator` to discover contributions from
+ * dependency modules during downstream compilation.
+ */
+public class ContributesConfigSelectorHintExtension(private val session: FirSession) :
+    MetroContributionHintExtension {
+
+    private val predicate = ContributesConfigSelectorIds.predicate
+
+    override fun FirDeclarationPredicateRegistrar.registerPredicates() {
+        register(predicate)
+    }
+
+    override fun getContributionHints(): List<ContributionHint> {
+        return session.predicateBasedProvider
+            .getSymbolsByPredicate(predicate)
+            .filterIsInstance<FirRegularClassSymbol>()
+            .map { classSymbol ->
+                val nestedInterfaceClassId = classSymbol.classId
+                    .createNestedClassId(ContributesConfigSelectorIds.nestedContributionName)
+                ContributionHint(
+                    contributingClassId = nestedInterfaceClassId,
+                    scope = ClassIds.appScope
+                )
+            }
+    }
+
+    public class Factory : MetroContributionHintExtension.Factory {
+        override fun create(
+            session: FirSession,
+            options: MetroOptions,
+            compatContext: CompatContext,
+        ): MetroContributionHintExtension {
+            return ContributesConfigSelectorHintExtension(session)
+        }
+    }
+}

compiler-plugin/src/com/bandlab/metro/station/entry/StationEntryHintExtension.kt

@@ -0,0 +1,71 @@
+package com.bandlab.metro.station.entry
+
+import com.bandlab.metro.station.graph.MetroStationIds
+import com.bandlab.metro.station.utils.ClassIds
+import com.bandlab.metro.station.utils.resolveParentScopeClassIdFromAnnotation
+import dev.zacsweers.metro.compiler.MetroOptions
+import dev.zacsweers.metro.compiler.api.fir.MetroContributionHintExtension
+import dev.zacsweers.metro.compiler.api.fir.MetroContributionHintExtension.ContributionHint
+import dev.zacsweers.metro.compiler.compat.CompatContext
+import org.jetbrains.kotlin.fir.FirSession
+import org.jetbrains.kotlin.fir.extensions.FirDeclarationPredicateRegistrar
+import org.jetbrains.kotlin.fir.extensions.predicateBasedProvider
+import org.jetbrains.kotlin.fir.symbols.impl.FirRegularClassSymbol
+import org.jetbrains.kotlin.name.ClassId
+
+/**
+ * Implements [MetroContributionHintExtension] to generate cross-module contribution hint files
+ * for `FeatureExtension.Factory` and `ExtensionFactoryContribution` interfaces generated by
+ * [StationEntryFir].
+ *
+ * These hint files allow Metro's `ContributionHintFirGenerator` to discover contributions from
+ * dependency modules during downstream compilation.
+ */
+public class StationEntryHintExtension(private val session: FirSession) : MetroContributionHintExtension {
+
+    private val predicate = MetroStationIds.stationEntryPredicate
+
+    override fun FirDeclarationPredicateRegistrar.registerPredicates() {
+        register(predicate)
+    }
+
+    override fun getContributionHints(): List<ContributionHint> {
+        return session.predicateBasedProvider
+            .getSymbolsByPredicate(predicate)
+            .filterIsInstance<FirRegularClassSymbol>()
+            .flatMap { classSymbol ->
+                val parentScope = resolveParentScopeClassId(classSymbol)
+                val factoryClassId = classSymbol.classId
+                    .createNestedClassId(MetroStationIds.featureExtensionName)
+                    .createNestedClassId(MetroStationIds.nestedFactoryName)
+                val extensionFactoryContributionClassId = classSymbol.classId
+                    .createNestedClassId(MetroStationIds.extensionFactoryContributionName)
+
+                // Always emit both hints. If ExtensionFactoryContribution wasn't generated
+                // (non-Fragment types), Metro's hint resolver safely skips non-existent classes.
+                listOf(
+                    ContributionHint(contributingClassId = factoryClassId, scope = parentScope),
+                    ContributionHint(contributingClassId = extensionFactoryContributionClassId, scope = parentScope),
+                )
+            }
+    }
+
+    private fun resolveParentScopeClassId(owner: FirRegularClassSymbol): ClassId {
+        return resolveParentScopeClassIdFromAnnotation(
+            owner,
+            MetroStationIds.stationEntry,
+            session,
+            ClassIds.appScope
+        )
+    }
+
+    public class Factory : MetroContributionHintExtension.Factory {
+        override fun create(
+            session: FirSession,
+            options: MetroOptions,
+            compatContext: CompatContext,
+        ): MetroContributionHintExtension {
+            return StationEntryHintExtension(session)
+        }
+    }
+}

compiler-plugin/src/com/bandlab/metro/station/graph/MetroStationHintExtension.kt

@@ -0,0 +1,48 @@
+package com.bandlab.metro.station.graph
+
+import com.bandlab.metro.station.utils.ClassIds
+import dev.zacsweers.metro.compiler.MetroOptions
+import dev.zacsweers.metro.compiler.api.fir.MetroContributionHintExtension
+import dev.zacsweers.metro.compiler.api.fir.MetroContributionHintExtension.ContributionHint
+import dev.zacsweers.metro.compiler.compat.CompatContext
+import org.jetbrains.kotlin.fir.FirSession
+import org.jetbrains.kotlin.fir.extensions.FirDeclarationPredicateRegistrar
+import org.jetbrains.kotlin.fir.extensions.predicateBasedProvider
+import org.jetbrains.kotlin.fir.symbols.impl.FirRegularClassSymbol
+
+/**
+ * Implements [MetroContributionHintExtension] to generate cross-module contribution hint files
+ * for `FeatureServiceProvider` interfaces generated by [MetroStationFir].
+ *
+ * These hint files allow Metro's `ContributionHintFirGenerator` to discover contributions from
+ * dependency modules during downstream compilation.
+ */
+public class MetroStationHintExtension(private val session: FirSession) : MetroContributionHintExtension {
+
+    private val predicate = MetroStationIds.metroStationPredicate
+
+    override fun FirDeclarationPredicateRegistrar.registerPredicates() {
+        register(predicate)
+    }
+
+    override fun getContributionHints(): List<ContributionHint> {
+        return session.predicateBasedProvider
+            .getSymbolsByPredicate(predicate)
+            .filterIsInstance<FirRegularClassSymbol>()
+            .map { classSymbol ->
+                val serviceProvider = classSymbol.classId
+                    .createNestedClassId(MetroStationIds.featureServiceProviderName)
+                ContributionHint(contributingClassId = serviceProvider, scope = ClassIds.appScope)
+            }
+    }
+
+    public class Factory : MetroContributionHintExtension.Factory {
+        override fun create(
+            session: FirSession,
+            options: MetroOptions,
+            compatContext: CompatContext,
+        ): MetroContributionHintExtension {
+            return MetroStationHintExtension(session)
+        }
+    }
+}

compiler-plugin/test-fixtures/com/bandlab/metro/station/services/ExtensionRegistrarConfigurator.kt

@@ -3,6 +3,7 @@ package com.bandlab.metro.station.services
 import com.bandlab.metro.station.MetroStationPluginRegistrar
 import com.bandlab.metro.station.entry.StationEntryIr
 import com.bandlab.metro.station.graph.MetroStationIr
+import dev.zacsweers.metro.compiler.MetroCommandLineProcessor
 import dev.zacsweers.metro.compiler.MetroCompilerPluginRegistrar
 import org.jetbrains.kotlin.backend.common.extensions.IrGenerationExtension
 import org.jetbrains.kotlin.compiler.plugin.CompilerPluginRegistrar
@@ -53,12 +54,23 @@ fun TestConfigurationBuilder.configureImports(
 }
 
 private class ExtensionRegistrarConfigurator(testServices: TestServices) : EnvironmentConfigurator(testServices) {
+
+    private val metroCliProcessor = MetroCommandLineProcessor()
     private val metroRegistrar = MetroCompilerPluginRegistrar()
 
     override fun CompilerPluginRegistrar.ExtensionStorage.registerCompilerExtensions(
         module: TestModule,
         configuration: CompilerConfiguration
     ) {
+        // Configure Metro options from directives before registering
+        if (MetroDirectives.GENERATE_CLASSES_IN_IR in module.directives) {
+            val option =
+                metroCliProcessor.pluginOptions.first {
+                    it.optionName == "generate-classes-in-ir"
+                }
+            metroCliProcessor.processOption(option, "true", configuration)
+        }
+
         val includeBaselineChecker = MetroDirectives.ENABLE_STATION_ENTRIES_BASELINE in module.directives
         FirExtensionRegistrarAdapter.registerExtension(
             MetroStationPluginRegistrar(

compiler-plugin/test-fixtures/com/bandlab/metro/station/services/MetroDirectives.kt

@@ -4,4 +4,5 @@ import org.jetbrains.kotlin.test.directives.model.SimpleDirectivesContainer
 
 object MetroDirectives : SimpleDirectivesContainer() {
     val ENABLE_STATION_ENTRIES_BASELINE by directive("Enable the StationEntry baseline checker.")
+    val GENERATE_CLASSES_IN_IR by directive("Generate the Classes in ir.")
 }

compiler-plugin/testData/dump/entry/activity/activityParam.fir.ir.txt

@@ -605,7 +605,7 @@ FILE fqName:<root> fileName:/activityParam.kt
       VALUE_PARAMETER kind:DispatchReceiver name:<this> index:0 type:kotlin.Any
       overridden:
         public open fun toString (): kotlin.String declared in kotlin.Any
-  CLASS INTERFACE name:AppGraph modality:ABSTRACT visibility:public superTypes:[kotlin.Any; <root>.MyActivity.FeatureExtension.Factory.MetroContributionToDevzacsweersmetroappScopeocf15; com.bandlab.common.android.di.GraphExtensionFactoriesProvider; com.bandlab.common.android.di.GraphExtensionFactoriesProvider.MetroContributionToAppScope]
+  CLASS INTERFACE name:AppGraph modality:ABSTRACT visibility:public superTypes:[kotlin.Any; <root>.MyActivity.FeatureExtension.Factory.MetroContributionToDevzacsweersmetroappScopeocf15]
     annotations:
       DependencyGraph(scope = AppScope::class, additionalScopes = <null>, excludes = <null>, bindingContainers = <null>)
     thisReceiver: VALUE_PARAMETER INSTANCE_RECEIVER kind:DispatchReceiver name:<this> type:<root>.AppGraph
@@ -702,21 +702,6 @@ FILE fqName:<root> fileName:/activityParam.kt
             CONSTRUCTOR_CALL 'public constructor <init> (appGraphImpl: <root>.AppGraph.Impl, feature: <root>.MyActivity) declared in <root>.AppGraph.Impl.FeatureExtensionImpl' type=<root>.AppGraph.Impl.FeatureExtensionImpl origin=null
               ARG appGraphImpl: GET_VAR '<this>: <root>.AppGraph.Impl declared in <root>.AppGraph.Impl.create' type=<root>.AppGraph.Impl origin=null
               ARG feature: GET_VAR 'feature: <root>.MyActivity declared in <root>.AppGraph.Impl.create' type=<root>.MyActivity origin=null
-      PROPERTY name:graphExtensionFactories visibility:public modality:FINAL [val]
-        annotations:
-          Multibinds(allowEmpty = true)
-        overridden:
-          public abstract graphExtensionFactories: kotlin.collections.Map<kotlin.reflect.KClass<*>, kotlin.Any> declared in <root>.AppGraph
-        FUN name:<get-graphExtensionFactories> visibility:public modality:FINAL returnType:kotlin.collections.Map<kotlin.reflect.KClass<*>, kotlin.Any>
-          VALUE_PARAMETER INSTANCE_RECEIVER kind:DispatchReceiver name:<this> index:0 type:<root>.AppGraph.Impl
-          correspondingProperty: PROPERTY name:graphExtensionFactories visibility:public modality:FINAL [val]
-          overridden:
-            public abstract fun <get-graphExtensionFactories> (): kotlin.collections.Map<kotlin.reflect.KClass<*>, kotlin.Any> declared in <root>.AppGraph
-          BLOCK_BODY
-            RETURN type=kotlin.Nothing from='public final fun <get-graphExtensionFactories> (): kotlin.collections.Map<kotlin.reflect.KClass<*>, kotlin.Any> declared in <root>.AppGraph.Impl'
-              CALL 'public final fun emptyMap <K, V> (): kotlin.collections.Map<K of kotlin.collections.emptyMap, V of kotlin.collections.emptyMap> declared in kotlin.collections' type=kotlin.collections.Map<kotlin.reflect.KClass<*>, kotlin.Any> origin=null
-                TYPE_ARG K: kotlin.reflect.KClass<*>
-                TYPE_ARG V: kotlin.Any
     CLASS GENERATED[dev.zacsweers.metro.compiler.fir.Keys.MetroGraphCreatorsObjectDeclaration] OBJECT name:Companion modality:FINAL visibility:public [companion] superTypes:[kotlin.Any]
       thisReceiver: VALUE_PARAMETER INSTANCE_RECEIVER kind:DispatchReceiver name:<this> type:<root>.AppGraph.Companion
       CONSTRUCTOR GENERATED[dev.zacsweers.metro.compiler.fir.Keys.Default] visibility:private returnType:<root>.AppGraph.Companion [primary]
@@ -757,32 +742,14 @@ FILE fqName:<root> fileName:/activityParam.kt
       VALUE_PARAMETER kind:Regular name:other index:1 type:kotlin.Any?
       overridden:
         public open fun equals (other: kotlin.Any?): kotlin.Boolean declared in kotlin.Any
-        public open fun equals (other: kotlin.Any?): kotlin.Boolean declared in com.bandlab.common.android.di.GraphExtensionFactoriesProvider
-        public open fun equals (other: kotlin.Any?): kotlin.Boolean declared in com.bandlab.common.android.di.GraphExtensionFactoriesProvider.MetroContributionToAppScope
     FUN FAKE_OVERRIDE name:hashCode visibility:public modality:OPEN returnType:kotlin.Int [fake_override]
       VALUE_PARAMETER kind:DispatchReceiver name:<this> index:0 type:kotlin.Any
       overridden:
         public open fun hashCode (): kotlin.Int declared in kotlin.Any
-        public open fun hashCode (): kotlin.Int declared in com.bandlab.common.android.di.GraphExtensionFactoriesProvider
-        public open fun hashCode (): kotlin.Int declared in com.bandlab.common.android.di.GraphExtensionFactoriesProvider.MetroContributionToAppScope
     FUN FAKE_OVERRIDE name:toString visibility:public modality:OPEN returnType:kotlin.String [fake_override]
       VALUE_PARAMETER kind:DispatchReceiver name:<this> index:0 type:kotlin.Any
       overridden:
         public open fun toString (): kotlin.String declared in kotlin.Any
-        public open fun toString (): kotlin.String declared in com.bandlab.common.android.di.GraphExtensionFactoriesProvider
-        public open fun toString (): kotlin.String declared in com.bandlab.common.android.di.GraphExtensionFactoriesProvider.MetroContributionToAppScope
-    PROPERTY FAKE_OVERRIDE name:graphExtensionFactories visibility:public modality:ABSTRACT [fake_override,val]
-      annotations:
-        Multibinds(allowEmpty = true)
-      overridden:
-        public abstract graphExtensionFactories: kotlin.collections.Map<kotlin.reflect.KClass<*>, kotlin.Any> declared in com.bandlab.common.android.di.GraphExtensionFactoriesProvider
-        public abstract graphExtensionFactories: kotlin.collections.Map<kotlin.reflect.KClass<*>, kotlin.Any> declared in com.bandlab.common.android.di.GraphExtensionFactoriesProvider.MetroContributionToAppScope
-      FUN FAKE_OVERRIDE name:<get-graphExtensionFactories> visibility:public modality:ABSTRACT returnType:kotlin.collections.Map<kotlin.reflect.KClass<*>, kotlin.Any> [fake_override]
-        VALUE_PARAMETER kind:DispatchReceiver name:<this> index:0 type:com.bandlab.common.android.di.GraphExtensionFactoriesProvider
-        correspondingProperty: PROPERTY FAKE_OVERRIDE name:graphExtensionFactories visibility:public modality:ABSTRACT [fake_override,val]
-        overridden:
-          public abstract fun <get-graphExtensionFactories> (): kotlin.collections.Map<kotlin.reflect.KClass<*>, kotlin.Any> declared in com.bandlab.common.android.di.GraphExtensionFactoriesProvider
-          public abstract fun <get-graphExtensionFactories> (): kotlin.collections.Map<kotlin.reflect.KClass<*>, kotlin.Any> declared in com.bandlab.common.android.di.GraphExtensionFactoriesProvider.MetroContributionToAppScope
 FILE fqName:metro.hints fileName:/myActivityFeatureExtensionFactoryAppScope.kt
   FUN GENERATED[dev.zacsweers.metro.compiler.fir.Keys.Default] name:AppScope visibility:public modality:FINAL returnType:kotlin.Unit
     VALUE_PARAMETER kind:Regular name:contributed index:0 type:<root>.MyActivity.FeatureExtension.Factory

compiler-plugin/testData/dump/entry/activity/activityParam.fir.kt.txt

@@ -290,7 +290,7 @@ class MyViewModel {
 }
 
 @DependencyGraph(scope = AppScope::class)
-interface AppGraph : MetroContributionToDevzacsweersmetroappScopeocf15, GraphExtensionFactoriesProvider, MetroContributionToAppScope {
+interface AppGraph : MetroContributionToDevzacsweersmetroappScopeocf15 {
   @Deprecated(message = "This synthesized declaration should not be used directly", level = DeprecationLevel.HIDDEN)
   @MetroImplMarker
   class Impl : AppGraph {
@@ -329,12 +329,6 @@ interface AppGraph : MetroContributionToDevzacsweersmetroappScopeocf15, GraphExt
       return FeatureExtensionImpl(appGraphImpl = <this>, feature = feature)
     }
 
-    @Multibinds(allowEmpty = true)
-    override val graphExtensionFactories: Map<KClass<*>, Any>
-      override get(): Map<KClass<*>, Any> {
-        return emptyMap<KClass<*>, Any>()
-      }
-
   }
 
   companion object Companion {