[MNG-8384] Make sure plugin's artifacts have a scope (#1928)

Author: gnodet

impl/maven-core/src/main/java/org/apache/maven/RepositoryUtils.java

@@ -69,7 +69,7 @@ private static String nullify(String string) {
         return (string == null || string.isEmpty()) ? null : string;
     }
 
-    private static org.apache.maven.artifact.Artifact toArtifact(Dependency dependency) {
+    public static org.apache.maven.artifact.Artifact toArtifact(Dependency dependency) {
         if (dependency == null) {
             return null;
         }

impl/maven-core/src/main/java/org/apache/maven/plugin/internal/DefaultMavenPluginManager.java

@@ -34,7 +34,6 @@
 import java.nio.file.Path;
 import java.util.ArrayList;
 import java.util.Collection;
-import java.util.Collections;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
@@ -121,7 +120,6 @@
 import org.eclipse.aether.RepositorySystemSession;
 import org.eclipse.aether.graph.DependencyFilter;
 import org.eclipse.aether.repository.RemoteRepository;
-import org.eclipse.aether.resolution.ArtifactResult;
 import org.eclipse.aether.resolution.DependencyResult;
 import org.eclipse.aether.util.filter.AndDependencyFilter;
 import org.slf4j.Logger;
@@ -463,12 +461,10 @@ private List<org.eclipse.aether.artifact.Artifact> toAetherArtifacts(final List<
     }
 
     private List<Artifact> toMavenArtifacts(DependencyResult dependencyResult) {
-        List<Artifact> artifacts =
-                new ArrayList<>(dependencyResult.getArtifactResults().size());
-        dependencyResult.getArtifactResults().stream()
-                .filter(ArtifactResult::isResolved)
-                .forEach(a -> artifacts.add(RepositoryUtils.toArtifact(a.getArtifact())));
-        return Collections.unmodifiableList(artifacts);
+        return dependencyResult.getDependencyNodeResults().stream()
+                .filter(n -> n.getArtifact().getPath() != null)
+                .map(n -> RepositoryUtils.toArtifact(n.getDependency()))
+                .collect(Collectors.toUnmodifiableList());
     }
 
     private Map<String, ClassLoader> calcImports(