[MNG-7251] Fix threadLocalArtifactsHolder leaking into cloned project

This closes #535

maven-core/src/main/java/org/apache/maven/project/MavenProject.java

@@ -147,8 +147,7 @@ public class MavenProject
 
     private Artifact artifact;
 
-    private final ThreadLocal<ArtifactsHolder> threadLocalArtifactsHolder =
-        ThreadLocal.withInitial( ArtifactsHolder::new );
+    private ThreadLocal<ArtifactsHolder> threadLocalArtifactsHolder = ThreadLocal.withInitial( ArtifactsHolder::new );
 
     private Model originalModel;
 
@@ -1177,7 +1176,8 @@ public class MavenProject
         {
             throw new UnsupportedOperationException( e );
         }
-
+        // clone must have its own TL, otherwise the artifacts are intermingled!
+        clone.threadLocalArtifactsHolder = ThreadLocal.withInitial( ArtifactsHolder::new );
         clone.deepCopy( this );
 
         return clone;
@@ -1220,6 +1220,7 @@ public class MavenProject
         // copy fields
         file = project.file;
         basedir = project.basedir;
+        threadLocalArtifactsHolder.set( project.threadLocalArtifactsHolder.get().copy() );
 
         // don't need a deep copy, they don't get modified or added/removed to/from - but make them unmodifiable to be
         // sure!
@@ -1228,11 +1229,6 @@ public class MavenProject
             setDependencyArtifacts( Collections.unmodifiableSet( project.getDependencyArtifacts() ) );
         }
 
-        if ( project.getArtifacts() != null )
-        {
-            setArtifacts( Collections.unmodifiableSet( project.getArtifacts() ) );
-        }
-
         if ( project.getParentFile() != null )
         {
             parentFile = new File( project.getParentFile().getAbsolutePath() );
@@ -1475,13 +1471,7 @@ public class MavenProject
 
     // ----------------------------------------------------------------------------------------------------------------
     //
-    //
-    // D E P R E C A T E D
-    //
-    //
-    // ----------------------------------------------------------------------------------------------------------------
-    //
-    // Everything below will be removed for Maven 4.0.0
+    // D E P R E C A T E D - Everything below will be removed for Maven 4.0.0
     //
     // ----------------------------------------------------------------------------------------------------------------
 
@@ -1502,7 +1492,6 @@ public class MavenProject
         if ( moduleFile != null )
         {
             File moduleDir = moduleFile.getCanonicalFile().getParentFile();
-
             module = moduleDir.getName();
         }
 
@@ -1823,7 +1812,6 @@ public class MavenProject
     public void setReportArtifacts( Set<Artifact> reportArtifacts )
     {
         this.reportArtifacts = reportArtifacts;
-
         reportArtifactMap = null;
     }
 
@@ -1847,7 +1835,6 @@ public class MavenProject
     public void setExtensionArtifacts( Set<Artifact> extensionArtifacts )
     {
         this.extensionArtifacts = extensionArtifacts;
-
         extensionArtifactMap = null;
     }
 
@@ -1881,7 +1868,6 @@ public class MavenProject
     public Xpp3Dom getReportConfiguration( String pluginGroupId, String pluginArtifactId, String reportSetId )
     {
         Xpp3Dom dom = null;
-
         // ----------------------------------------------------------------------
         // I would like to be able to lookup the Mojo object using a key but
         // we have a limitation in modello that will be remedied shortly. So
@@ -1991,5 +1977,14 @@ public class MavenProject
         private ArtifactFilter artifactFilter;
         private Set<Artifact> artifacts;
         private Map<String, Artifact> artifactMap;
+
+        ArtifactsHolder copy()
+        {
+           ArtifactsHolder copy = new ArtifactsHolder();
+           copy.artifactFilter = artifactFilter;
+           copy.artifacts = artifacts != null ? new LinkedHashSet<>( artifacts ) : null;
+           copy.artifactMap = artifactMap != null ? new LinkedHashMap<>( artifactMap ) : null;
+           return copy;
+        }
     }
 }

maven-core/src/test/java/org/apache/maven/project/MavenProjectTest.java

@@ -21,14 +21,19 @@ package org.apache.maven.project;
 
 import java.io.File;
 import java.io.IOException;
+import java.util.Collections;
 import java.util.List;
 import java.util.Map;
+import java.util.Set;
+import java.util.concurrent.atomic.AtomicReference;
 
+import org.apache.maven.artifact.Artifact;
 import org.apache.maven.model.DependencyManagement;
 import org.apache.maven.model.Model;
 import org.apache.maven.model.Parent;
 import org.apache.maven.model.Profile;
 import org.junit.jupiter.api.Test;
+import org.mockito.Mockito;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
@@ -204,6 +209,44 @@ public class MavenProjectTest
     }
 
     @Test
+    public void testCloneWithArtifacts()
+        throws InterruptedException
+    {
+        Artifact initialArtifact = Mockito.mock( Artifact.class, "initialArtifact" );
+        MavenProject originalProject = new MavenProject();
+        originalProject.setArtifacts( Collections.singleton( initialArtifact ) );
+        assertEquals( Collections.singleton( initialArtifact ), originalProject.getArtifacts(),
+                      "Sanity check: originalProject returns artifact that has just been set" );
+
+        final MavenProject clonedProject = originalProject.clone();
+
+        assertEquals( Collections.singleton( initialArtifact ), clonedProject.getArtifacts(),
+                      "Cloned project returns the artifact that was set for the original project" );
+
+        Artifact anotherArtifact = Mockito.mock( Artifact.class, "anotherArtifact" );
+        clonedProject.setArtifacts( Collections.singleton( anotherArtifact ) );
+        assertEquals( Collections.singleton( anotherArtifact ), clonedProject.getArtifacts(),
+                      "Sanity check: clonedProject returns artifact that has just been set" );
+
+        assertEquals( Collections.singleton( initialArtifact ), originalProject.getArtifacts(),
+                      "Original project returns the artifact that was set initially (not the one for clonedProject)" );
+
+        final AtomicReference<Set<Artifact>> artifactsFromThread = new AtomicReference<>();
+        Thread thread = new Thread( new Runnable()
+        {
+            @Override
+            public void run()
+            {
+                artifactsFromThread.set( clonedProject.getArtifacts() );
+            }
+        } );
+        thread.start();
+        thread.join();
+
+        assertEquals( Collections.emptySet(), artifactsFromThread.get(),
+                      "Another thread does not see the same artifacts" );
+    }
+
     public void testUndefinedOutputDirectory()
         throws Exception
     {