Remove empty dependency scope from the api (#1402)

api/maven-api-core/src/main/java/org/apache/maven/api/DependencyScope.java

@@ -49,9 +49,12 @@ public enum DependencyScope {
     NONE("none", false),
 
     /**
-     * Empty scope.
+     * Undefined. When no scope is explicitly given, UNDEFINED will be used, but its meaning will depend on
+     * whether the DependencyCoordinate is used in dependency management, in which case it means the scope is not
+     * explicitly managed by this managed dependency, or as a real dependency, in which case, the scope
+     * will default to {@link #COMPILE}.
      */
-    EMPTY("", false),
+    UNDEFINED("", false),
 
     /**
      * Compile only.

api/maven-api-core/src/main/java/org/apache/maven/api/PathScope.java

@@ -55,18 +55,16 @@ public interface PathScope extends ExtensibleEnum {
     PathScope MAIN_COMPILE = pathScope(
             "main-compile",
             ProjectScope.MAIN,
-            DependencyScope.EMPTY,
             DependencyScope.COMPILE_ONLY,
             DependencyScope.COMPILE,
             DependencyScope.PROVIDED);
 
-    PathScope MAIN_RUNTIME = pathScope(
+    PathScope MAIN_RUNTIME =
-            "main-runtime", ProjectScope.MAIN, DependencyScope.EMPTY, DependencyScope.COMPILE, DependencyScope.RUNTIME);
+            pathScope("main-runtime", ProjectScope.MAIN, DependencyScope.COMPILE, DependencyScope.RUNTIME);
 
     PathScope TEST_COMPILE = pathScope(
             "test-compile",
             ProjectScope.TEST,
-            DependencyScope.EMPTY,
             DependencyScope.COMPILE,
             DependencyScope.PROVIDED,
             DependencyScope.TEST_ONLY,
@@ -75,7 +73,6 @@ public interface PathScope extends ExtensibleEnum {
     PathScope TEST_RUNTIME = pathScope(
             "test-runtime",
             ProjectScope.TEST,
-            DependencyScope.EMPTY,
             DependencyScope.COMPILE,
             DependencyScope.RUNTIME,
             DependencyScope.PROVIDED,

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

@@ -111,11 +111,12 @@ public abstract class AbstractSession implements InternalSession {
 
     public abstract ArtifactRepository toArtifactRepository(RemoteRepository repository);
 
-    public List<org.eclipse.aether.graph.Dependency> toDependencies(Collection<DependencyCoordinate> dependencies) {
+    public List<org.eclipse.aether.graph.Dependency> toDependencies(
-        return dependencies == null ? null : map(dependencies, this::toDependency);
+            Collection<DependencyCoordinate> dependencies, boolean managed) {
+        return dependencies == null ? null : map(dependencies, d -> toDependency(d, managed));
     }
 
-    public abstract org.eclipse.aether.graph.Dependency toDependency(DependencyCoordinate dependency);
+    public abstract org.eclipse.aether.graph.Dependency toDependency(DependencyCoordinate dependency, boolean managed);
 
     public List<org.eclipse.aether.artifact.Artifact> toArtifacts(Collection<Artifact> artifacts) {
         return artifacts == null ? null : map(artifacts, this::toArtifact);

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

@@ -54,12 +54,13 @@ public class DefaultDependencyCollector implements DependencyCollector {
 
         Artifact rootArtifact =
                 request.getRootArtifact().map(session::toArtifact).orElse(null);
-        Dependency root = request.getRoot().map(session::toDependency).orElse(null);
+        Dependency root =
+                request.getRoot().map(d -> session.toDependency(d, false)).orElse(null);
         CollectRequest collectRequest = new CollectRequest()
                 .setRootArtifact(rootArtifact)
                 .setRoot(root)
-                .setDependencies(session.toDependencies(request.getDependencies()))
+                .setDependencies(session.toDependencies(request.getDependencies(), false))
-                .setManagedDependencies(session.toDependencies(request.getManagedDependencies()))
+                .setManagedDependencies(session.toDependencies(request.getManagedDependencies(), true))
                 .setRepositories(session.toRepositories(session.getRemoteRepositories()));
 
         RepositorySystemSession systemSession = session.getSession();

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

@@ -280,11 +280,12 @@ public class DefaultSession extends AbstractSession {
         }
     }
 
-    public org.eclipse.aether.graph.Dependency toDependency(DependencyCoordinate dependency) {
+    public org.eclipse.aether.graph.Dependency toDependency(DependencyCoordinate dependency, boolean managed) {
+        org.eclipse.aether.graph.Dependency dep;
         if (dependency instanceof DefaultDependencyCoordinate) {
-            return ((DefaultDependencyCoordinate) dependency).getDependency();
+            dep = ((DefaultDependencyCoordinate) dependency).getDependency();
         } else {
-            return new org.eclipse.aether.graph.Dependency(
+            dep = new org.eclipse.aether.graph.Dependency(
                     new org.eclipse.aether.artifact.DefaultArtifact(
                             dependency.getGroupId(),
                             dependency.getArtifactId(),
@@ -294,5 +295,9 @@ public class DefaultSession extends AbstractSession {
                             null),
                     dependency.getScope().id());
         }
+        if (!managed && "".equals(dep.getScope())) {
+            dep = dep.setScope(DependencyScope.COMPILE.id());
+        }
+        return dep;
     }
 }

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

@@ -70,9 +70,10 @@ public interface InternalSession extends Session {
 
     org.apache.maven.artifact.repository.ArtifactRepository toArtifactRepository(RemoteRepository repository);
 
-    List<org.eclipse.aether.graph.Dependency> toDependencies(Collection<DependencyCoordinate> dependencies);
+    List<org.eclipse.aether.graph.Dependency> toDependencies(
+            Collection<DependencyCoordinate> dependencies, boolean managed);
 
-    org.eclipse.aether.graph.Dependency toDependency(DependencyCoordinate dependency);
+    org.eclipse.aether.graph.Dependency toDependency(DependencyCoordinate dependency, boolean managed);
 
     List<org.eclipse.aether.artifact.Artifact> toArtifacts(Collection<Artifact> artifacts);