Add overload for dependsOn

libraries/apollo-gradle-plugin-external/src/main/kotlin/com/apollographql/apollo3/gradle/api/Service.kt

@@ -766,11 +766,36 @@ interface Service {
   fun operationManifestConnection(action: Action<in OperationManifestConnection>)
 
   /**
-   * Adds a given dependency for the codegen
+   * Adds a dependency for the codegen. Use this when some types/fragments are generated
+   * in upstream modules.
    */
   fun dependsOn(dependencyNotation: Any)
+
+  /**
+   * Counterpoint of [dependsOn]. [isADependencyOf] allows a schema module to discover
+   * used types in downstream modules automatically without having to specify [alwaysGenerateTypesMatching].
+   *
+   * This works by setting a dependency on the IR in downstream modules.
+   * Because the IR task and the codegen task are separate this does not create a cycle.
+   *
+   * @see [alwaysGenerateTypesMatching]
+   */
   fun isADependencyOf(dependencyNotation: Any)
 
+  /**
+   * Same as [dependsOn] but tries to do automatic cross-project configuration.
+   * This is highly experimental and probably not compatible with most Gradle best practices.
+   *
+   * Use at your own risks!
+   *
+   * @param bidirectional if true and if [dependencyNotation] is a project dependency,
+   * this version of [dependsOn] also calls [isADependencyOf] automatically by using
+   * cross-project configuration. This is experimental and probably not project isolation compatible.
+   *
+   */
+  @ApolloExperimental
+  fun dependsOn(dependencyNotation: Any, bidirectional: Boolean)
+
   class OperationOutputConnection(
       /**
        * The task that produces operationOutput

libraries/apollo-gradle-plugin-external/src/main/kotlin/com/apollographql/apollo3/gradle/internal/DefaultApolloExtension.kt

@@ -54,6 +54,7 @@ abstract class DefaultApolloExtension(
   private var hasExplicitService = false
   private val adhocComponentWithVariants: AdhocComponentWithVariants
   private val apolloMetadataConfiguration: Configuration
+  private val pendingDownstreamDependencies: MutableMap<String, List<String>> = mutableMapOf()
 
   internal fun getServiceInfos(project: Project): List<ApolloGradleToolingModel.ServiceInfo> = services.map { service ->
     DefaultServiceInfo(
@@ -66,6 +67,19 @@ abstract class DefaultApolloExtension(
     )
   }
 
+  internal fun registerDownstreamProject(serviceName: String, projectPath: String) {
+    val existingService = services.firstOrNull {
+      it.name == serviceName
+    }
+    if (existingService != null) {
+      existingService.isADependencyOf(project.rootProject.project(projectPath))
+    } else {
+      pendingDownstreamDependencies.compute(serviceName) { _, oldValue ->
+        oldValue.orEmpty() + projectPath
+      }
+    }
+  }
+
   internal fun getServiceTelemetryData(): List<ApolloGradleToolingModel.TelemetryData.ServiceTelemetryData> = services.map { service ->
     DefaultServiceTelemetryData(
         codegenModels = service.codegenModels.orNull,
@@ -545,6 +559,13 @@ abstract class DefaultApolloExtension(
         upstreamIrConsumerConfiguration.dependencies.add(it)
         codegenMetadataConsumerConfiguration.dependencies.add(it)
       }
+
+      val pending = pendingDownstreamDependencies.get(name)
+      if (pending != null) {
+        pending.forEach {
+          service.isADependencyOf(project.project(it))
+        }
+      }
       service.downstreamDependencies.forEach {
         downstreamIrConsumerConfiguration.dependencies.add(it)
       }

libraries/apollo-gradle-plugin-external/src/main/kotlin/com/apollographql/apollo3/gradle/internal/DefaultService.kt

@@ -1,13 +1,15 @@
 package com.apollographql.apollo3.gradle.internal
 
 import com.apollographql.apollo3.annotations.ApolloDeprecatedSince
+import com.apollographql.apollo3.gradle.api.ApolloExtension
 import com.apollographql.apollo3.gradle.api.Introspection
 import com.apollographql.apollo3.gradle.api.RegisterOperationsConfig
 import com.apollographql.apollo3.gradle.api.Registry
 import com.apollographql.apollo3.gradle.api.Service
 import org.gradle.api.Action
 import org.gradle.api.Project
 import org.gradle.api.artifacts.Dependency
+import org.gradle.api.artifacts.ProjectDependency
 import org.gradle.api.file.ConfigurableFileTree
 import org.gradle.api.file.FileCollection
 import org.gradle.api.file.RegularFileProperty
@@ -188,7 +190,26 @@ abstract class DefaultService @Inject constructor(val project: Project, override
   override fun mapScalarToUpload(graphQLName: String) = mapScalar(graphQLName, "com.apollographql.apollo3.api.Upload", "com.apollographql.apollo3.api.UploadAdapter")
 
   override fun dependsOn(dependencyNotation: Any) {
+    dependsOn(dependencyNotation, false)
+  }
+
+  override fun dependsOn(dependencyNotation: Any, bidirectional: Boolean) {
     upstreamDependencies.add(project.dependencies.create(dependencyNotation))
+    if (bidirectional) {
+      val upstreamProject = when (dependencyNotation) {
+        is ProjectDependency -> project.rootProject.project(dependencyNotation.dependencyProject.path)
+        is Project -> dependencyNotation
+        else -> error("dependsOn(dependencyNotation, true) requires a Project or ProjectDependency")
+      }
+
+      upstreamProject.plugins.withId("com.apollographql.apollo3") {
+        val apolloExtension = (upstreamProject.extensions.findByType(ApolloExtension::class.java) as? DefaultApolloExtension)
+        check(apolloExtension != null) {
+          "Cannot find 'apollo' extension in upstream project ${upstreamProject.name} (registered: ${upstreamProject.extensions})"
+        }
+        apolloExtension.registerDownstreamProject(name, project.path)
+      }
+    }
   }
 
   override fun isADependencyOf(dependencyNotation: Any) {

tests/multi-module-1/bidirectional/build.gradle.kts

@@ -0,0 +1,19 @@
+plugins {
+  id("org.jetbrains.kotlin.jvm")
+  id("com.apollographql.apollo3")
+}
+
+apolloTest()
+
+dependencies {
+  implementation(libs.apollo.runtime)
+  implementation(project(":multi-module-1-root"))
+  testImplementation(libs.kotlin.test.junit)
+}
+
+apollo {
+  service("service") {
+    packageNamesFromFilePaths()
+    dependsOn(project(":multi-module-1-root"), true)
+  }
+}

tests/multi-module-1/bidirectional/src/main/graphql/com/example/operations.graphql

@@ -0,0 +1,6 @@
+query GetA {
+  a {
+    foo
+  }
+
+}

tests/multi-module-1/root/build.gradle.kts

@@ -7,6 +7,7 @@ apolloTest()
 
 dependencies {
   implementation(libs.apollo.runtime)
+  testImplementation(libs.kotlin.test)
 }
 
 apollo {

tests/multi-module-1/root/src/main/graphql/schema.graphqls

@@ -1,5 +1,15 @@
 type Query {
   long: Long!
+  a: A
+  b: B
+}
+
+type A {
+  foo: Int
+}
+
+type B {
+  foo: Int
 }
 
 scalar Long

tests/multi-module-1/root/src/test/kotlin/MainTest.kt

@@ -1,5 +1,16 @@
+import kotlin.test.Test
+
 class MainTest {
+  @Test
   fun test() {
     println(multimodule1.root.fragment.QueryDetails::class.java)
+    // A is used in the bidirectional module and registered automatically
+    println(multimodule1.root.type.A::class.java)
+    // B is not used at all and must not be generated
+    try {
+      val clazz = Class.forName("multimodule1.root.type.B")
+      error("An exception was expected but got $clazz instead")
+    } catch (e: ClassNotFoundException) {
+    }
   }
 }