Display an error if the aggregation is empty

nmcp/api/nmcp.api

@@ -19,6 +19,7 @@ public abstract class nmcp/LocalRepositoryOptions {
 public abstract interface class nmcp/NmcpAggregationExtension {
 	public abstract fun centralPortal (Lorg/gradle/api/Action;)V
 	public abstract fun getAllFiles ()Lorg/gradle/api/file/FileCollection;
+	public abstract fun getAllowEmptyAggregation ()Lorg/gradle/api/provider/Property;
 	public abstract fun localRepository (Lorg/gradle/api/Action;)V
 	public abstract fun publishAllProjectsProbablyBreakingProjectIsolation ()V
 }

nmcp/src/main/kotlin/nmcp/NmcpAggregationExtension.kt

@@ -2,6 +2,7 @@ package nmcp
 
 import org.gradle.api.Action
 import org.gradle.api.file.FileCollection
+import org.gradle.api.provider.Property
 
 interface NmcpAggregationExtension {
     /**
@@ -37,4 +38,10 @@ interface NmcpAggregationExtension {
      * Storage and or AWS S3.
      */
     val allFiles: FileCollection
+
+    /**
+     * By default, Nmcp errors if the aggregation is empty.
+     * Set this to true to allow empty aggregations.
+     */
+    val allowEmptyAggregation: Property<Boolean>
 }

nmcp/src/main/kotlin/nmcp/internal/DefaultNmcpAggregationExtension.kt

@@ -14,6 +14,7 @@ import org.gradle.api.artifacts.result.ArtifactResult
 import org.gradle.api.artifacts.result.ResolvedArtifactResult
 import org.gradle.api.attributes.Usage
 import org.gradle.api.file.ConfigurableFileCollection
+import org.gradle.api.provider.Property
 
 @GExtension(
     pluginId = "com.gradleup.nmcp.aggregation",
@@ -58,6 +59,12 @@ internal abstract class DefaultNmcpAggregationExtension(private val project: Pro
                 }
                 allNames.add(it.name.lowercase())
             }
+
+            if (!allowEmptyAggregation.orElse(false).get()) {
+                check(consumerConfiguration.dependencies.isNotEmpty()) {
+                    "Nmcp: the aggregation is empty. This is usually a misconfiguration. If this is intentional, set `allowEmptyAggregation` to true."
+                }
+            }
         }
     }
 
@@ -90,6 +97,8 @@ internal abstract class DefaultNmcpAggregationExtension(private val project: Pro
             }
         }
     }
+
+    abstract override val allowEmptyAggregation: Property<Boolean>
 }
 
 private fun isCompatible(artifactResult: ArtifactResult): Boolean {

nmcp/src/test/kotlin/DuplicateNameTest.kt → nmcp/src/test/kotlin/MainTest.kt

@@ -2,7 +2,7 @@ import java.io.File
 import kotlin.test.Test
 import org.gradle.testkit.runner.GradleRunner
 
-class DuplicateNameTest {
+class MainTest {
   @Test
   fun duplicateName() {
     val dst = File("build/testProject")
@@ -16,9 +16,26 @@ class DuplicateNameTest {
       val result = GradleRunner.create()
           .withProjectDir(dst)
           .withArguments("nmcpZipAggregation")
-          .forwardOutput()
           .buildAndFail()
 
       assert(result.output.contains("duplicate project name"))
   }
+
+    @Test
+    fun emptyAggregation() {
+        val dst = File("build/testProject")
+        val src = File("testProjects/empty-aggregation")
+
+        dst.deleteRecursively()
+        dst.mkdirs()
+
+        src.copyRecursively(dst, overwrite = true)
+
+        val result = GradleRunner.create()
+            .withProjectDir(dst)
+            .withArguments("help")
+            .buildAndFail()
+
+        assert(result.output.contains("Nmcp: the aggregation is empty"))
+    }
 }

nmcp/testProjects/empty-aggregation/build.gradle.kts

@@ -0,0 +1,3 @@
+plugins {
+  id("com.gradleup.nmcp.aggregation").version("1.4.2-SNAPSHOT")
+}

nmcp/testProjects/empty-aggregation/settings.gradle.kts

@@ -0,0 +1,6 @@
+pluginManagement {
+  listOf(repositories, dependencyResolutionManagement.repositories).forEach {
+    it.mavenCentral()
+    it.maven("../../../build/m2")
+  }
+}