feat: gradle plugin markers are the preferred way to depend on a plugin.

Author: autonomousapps

src/functionalTest/groovy/com/autonomousapps/jvm/BuildLogicSpec.groovy

@@ -9,18 +9,19 @@ import static com.google.common.truth.Truth.assertThat
 
 final class BuildLogicSpec extends AbstractJvmSpec {
 
-  def "gradle plugin markers are used when the plugin is used (#gradleVersion)"() {
+  // This ensures that plugin dependencies preferable reference the marker artifact.
+  def "gradle plugin markers are used when the plugin is used (#gradleVersion isDirect=#isDirect)"() {
     given:
-    def project = new BuildLogicProject()
+    def project = new BuildLogicProject(isDirect)
     gradleProject = project.gradleProject
 
     when:
     build(gradleVersion, gradleProject.rootDir, 'buildHealth')
 
     then:
-    assertThat(project.actualBuildHealth()).containsExactlyElementsIn(project.expectedBuildHealth)
+    assertThat(project.actualBuildHealth()).containsExactlyElementsIn(project.expectedBuildHealth())
 
     where:
-    gradleVersion << gradleVersions()
+    [gradleVersion, isDirect] << multivariableDataPipe(gradleVersions(), [true, false])
   }
 }

src/functionalTest/groovy/com/autonomousapps/jvm/projects/BuildLogicProject.groovy

@@ -5,23 +5,26 @@ package com.autonomousapps.jvm.projects
 import com.autonomousapps.AbstractProject
 import com.autonomousapps.kit.GradleProject
 import com.autonomousapps.kit.Source
-import com.autonomousapps.kit.SourceType
 import com.autonomousapps.kit.gradle.Dependency
 import com.autonomousapps.kit.gradle.Plugin
 import com.autonomousapps.kit.gradle.dependencies.Plugins
+import com.autonomousapps.model.Advice
 import com.autonomousapps.model.ProjectAdvice
 
-import static com.autonomousapps.AdviceHelper.actualProjectAdvice
-import static com.autonomousapps.AdviceHelper.emptyProjectAdviceFor
+import static com.autonomousapps.AdviceHelper.*
+import static com.autonomousapps.kit.gradle.Dependency.api
 import static com.autonomousapps.kit.gradle.Dependency.implementation
 
 final class BuildLogicProject extends AbstractProject {
 
-  private static final Dependency DAGP = implementation('com.autonomousapps.dependency-analysis:com.autonomousapps.dependency-analysis.gradle.plugin:3.9.0')
+  private static final Dependency DAGP = api('com.autonomousapps.dependency-analysis:com.autonomousapps.dependency-analysis.gradle.plugin:3.9.0')
+  private static final String PROVIDES_DAGP = ':provides-dagp'
 
+  private final boolean isDirect
   final GradleProject gradleProject
 
-  BuildLogicProject() {
+  BuildLogicProject(boolean isDirect) {
+    this.isDirect = isDirect
     this.gradleProject = build()
   }
 
@@ -31,20 +34,34 @@ final class BuildLogicProject extends AbstractProject {
         s.sources = sources
         s.withBuildScript { bs ->
           bs.plugins(Plugin.javaGradle, Plugins.kotlinJvmNoVersion, Plugins.dependencyAnalysisNoVersion)
+          bs.dependencies(dependencies())
+        }
+      }
+      .withSubproject(PROVIDES_DAGP) { s ->
+        s.withBuildScript { bs ->
+          bs.plugins(Plugin.javaLibrary)
           bs.dependencies(DAGP)
         }
       }
       .write()
   }
 
+  private Dependency dependencies() {
+    if (isDirect) {
+      DAGP
+    } else {
+      implementation(PROVIDES_DAGP)
+    }
+  }
+
   private List<Source> sources = [
     Source.kotlin(
       '''\
         package mutual.aid
         
         import com.autonomousapps.DependencyAnalysisSubExtension
         
-        class DagpConfigurer(private val dependencyAnalysis: DependencyAnalysisSubExtension)
+        class DagpConfigurer(val dependencyAnalysis: DependencyAnalysisSubExtension)
       '''.stripIndent()
     ).build()
   ]
@@ -53,7 +70,20 @@ final class BuildLogicProject extends AbstractProject {
     return actualProjectAdvice(gradleProject)
   }
 
-  final Set<ProjectAdvice> expectedBuildHealth = [
-    emptyProjectAdviceFor(':conventions'),
-  ]
+  private Set<Advice> conventionsAdvice() {
+    if (isDirect) {
+      []
+    } else {
+      [
+        Advice.ofAdd(moduleCoordinates(DAGP), 'api'),
+        Advice.ofRemove(projectCoordinates(PROVIDES_DAGP), 'implementation')
+      ]
+    }
+  }
+
+  final Set<ProjectAdvice> expectedBuildHealth() {
+    [
+      projectAdviceForDependencies(':conventions', conventionsAdvice()),
+    ]
+  }
 }

src/main/kotlin/com/autonomousapps/internal/Bundles.kt

@@ -191,6 +191,8 @@ internal class Bundles private constructor(
   }
 
   companion object {
+    private const val GRADLE_PLUGIN_MARKER_SUFFIX = ".gradle.plugin"
+
     fun of(
       projectPath: String,
       dependencyGraph: Map<String, DependencyGraphView>,
@@ -249,7 +251,7 @@ internal class Bundles private constructor(
           }
 
           // handle Gradle plugin marker artifacts
-          if (parentNode.identifier.endsWith(".gradle.plugin")) {
+          if (parentNode.identifier.endsWith(GRADLE_PLUGIN_MARKER_SUFFIX)) {
             view.graph.children(parentNode)
               .singleOrNull()
               ?.let { child -> bundles[parentNode] = child }
@@ -267,6 +269,21 @@ internal class Bundles private constructor(
           implicitKmpBundleFor("android")
         }
 
+        // handle Gradle plugin marker artifacts buried in the graph
+        view.graph.nodes()
+          .filter { node -> node.identifier.endsWith(GRADLE_PLUGIN_MARKER_SUFFIX) }
+          .mapNotNull { markerArtifact ->
+            val plugin = view.graph.children(markerArtifact).singleOrNull()
+            if (plugin != null) {
+              markerArtifact to plugin
+            } else {
+              null
+            }
+          }
+          .forEach { (markerArtifact, plugin) ->
+            bundles.setPrimary(markerArtifact, plugin)
+          }
+
         fun implicitKmpPrimaryFor(target: String) {
           val suffix = "-$target"
           view.graph.nodes()