[MRESOLVER-451] Tidy up version filters

maven-resolver-util/src/main/java/org/eclipse/aether/util/graph/version/ChainedVersionFilter.java

@@ -88,12 +88,14 @@ private ChainedVersionFilter(VersionFilter[] filters) {
         this.filters = filters;
     }
 
+    @Override
     public void filterVersions(VersionFilterContext context) throws RepositoryException {
         for (int i = 0, n = filters.length; i < n && context.getCount() > 0; i++) {
             filters[i].filterVersions(context);
         }
     }
 
+    @Override
     public VersionFilter deriveChildFilter(DependencyCollectionContext context) {
         VersionFilter[] children = null;
         int removed = 0;

maven-resolver-util/src/main/java/org/eclipse/aether/util/graph/version/ContextualSnapshotVersionFilter.java

@@ -57,12 +57,14 @@ private boolean isEnabled(RepositorySystemSession session) {
         return ConfigUtils.getBoolean(session, false, CONFIG_PROP_ENABLE);
     }
 
+    @Override
     public void filterVersions(VersionFilterContext context) {
         if (isEnabled(context.getSession())) {
             filter.filterVersions(context);
         }
     }
 
+    @Override
     public VersionFilter deriveChildFilter(DependencyCollectionContext context) {
         if (!isEnabled(context.getSession())) {
             Artifact artifact = context.getArtifact();

maven-resolver-util/src/main/java/org/eclipse/aether/util/graph/version/HighestVersionFilter.java

@@ -34,6 +34,7 @@ public final class HighestVersionFilter implements VersionFilter {
      */
     public HighestVersionFilter() {}
 
+    @Override
     public void filterVersions(VersionFilterContext context) {
         Iterator<Version> it = context.iterator();
         for (boolean hasNext = it.hasNext(); hasNext; ) {
@@ -45,6 +46,7 @@ public void filterVersions(VersionFilterContext context) {
         }
     }
 
+    @Override
     public VersionFilter deriveChildFilter(DependencyCollectionContext context) {
         return this;
     }

maven-resolver-util/src/main/java/org/eclipse/aether/util/graph/version/LowestVersionFilter.java

@@ -0,0 +1,70 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.eclipse.aether.util.graph.version;
+
+import java.util.Iterator;
+
+import org.eclipse.aether.collection.DependencyCollectionContext;
+import org.eclipse.aether.collection.VersionFilter;
+import org.eclipse.aether.version.Version;
+
+/**
+ * A version filter that excludes any version except the lowest one.
+ *
+ * @since 2.0.0
+ */
+public final class LowestVersionFilter implements VersionFilter {
+
+    /**
+     * Creates a new instance of this version filter.
+     */
+    public LowestVersionFilter() {}
+
+    @Override
+    public void filterVersions(VersionFilterContext context) {
+        Iterator<Version> it = context.iterator();
+        if (it.hasNext()) {
+            it.next();
+            while (it.hasNext()) {
+                it.next();
+                it.remove();
+            }
+        }
+    }
+
+    @Override
+    public VersionFilter deriveChildFilter(DependencyCollectionContext context) {
+        return this;
+    }
+
+    @Override
+    public boolean equals(Object obj) {
+        if (this == obj) {
+            return true;
+        } else if (null == obj || !getClass().equals(obj.getClass())) {
+            return false;
+        }
+        return true;
+    }
+
+    @Override
+    public int hashCode() {
+        return getClass().hashCode();
+    }
+}

maven-resolver-util/src/main/java/org/eclipse/aether/util/graph/version/PredicateVersionFilter.java

@@ -0,0 +1,80 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.eclipse.aether.util.graph.version;
+
+import java.util.Iterator;
+import java.util.Objects;
+import java.util.function.Predicate;
+
+import org.eclipse.aether.artifact.Artifact;
+import org.eclipse.aether.collection.DependencyCollectionContext;
+import org.eclipse.aether.collection.VersionFilter;
+import org.eclipse.aether.version.Version;
+
+import static java.util.Objects.requireNonNull;
+
+/**
+ * A version filter that excludes any version that is blacklisted.
+ *
+ * @since 2.0.0
+ */
+public final class PredicateVersionFilter implements VersionFilter {
+    private final Predicate<Artifact> artifactPredicate;
+
+    /**
+     * Creates a new instance of this version filter.
+     */
+    public PredicateVersionFilter(Predicate<Artifact> artifactPredicate) {
+        this.artifactPredicate = requireNonNull(artifactPredicate);
+    }
+
+    @Override
+    public void filterVersions(VersionFilterContext context) {
+        Artifact dependencyArtifact = context.getDependency().getArtifact();
+        Iterator<Version> it = context.iterator();
+        while (it.hasNext()) {
+            Version version = it.next();
+            if (!artifactPredicate.test(dependencyArtifact.setVersion(version.toString()))) {
+                it.remove();
+            }
+        }
+    }
+
+    @Override
+    public VersionFilter deriveChildFilter(DependencyCollectionContext context) {
+        return this;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) {
+            return true;
+        }
+        if (o == null || getClass() != o.getClass()) {
+            return false;
+        }
+        PredicateVersionFilter that = (PredicateVersionFilter) o;
+        return Objects.equals(artifactPredicate, that.artifactPredicate);
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(artifactPredicate);
+    }
+}

maven-resolver-util/src/main/java/org/eclipse/aether/util/graph/version/SnapshotVersionFilter.java

@@ -35,6 +35,7 @@ public final class SnapshotVersionFilter implements VersionFilter {
      */
     public SnapshotVersionFilter() {}
 
+    @Override
     public void filterVersions(VersionFilterContext context) {
         for (Iterator<Version> it = context.iterator(); it.hasNext(); ) {
             String version = it.next().toString();
@@ -44,6 +45,7 @@ public void filterVersions(VersionFilterContext context) {
         }
     }
 
+    @Override
     public VersionFilter deriveChildFilter(DependencyCollectionContext context) {
         return this;
     }

maven-resolver-util/src/test/java/org/eclipse/aether/util/graph/versions/LowestVersionFilterTest.java

@@ -0,0 +1,51 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.eclipse.aether.util.graph.versions;
+
+import org.eclipse.aether.collection.VersionFilter.VersionFilterContext;
+import org.eclipse.aether.util.graph.version.LowestVersionFilter;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+public class LowestVersionFilterTest extends AbstractVersionFilterTest {
+
+    @Test
+    void testFilterVersions() {
+        LowestVersionFilter filter = new LowestVersionFilter();
+        VersionFilterContext ctx = newContext("g:a:[1,9]", "1", "2", "3", "4", "5", "6", "7", "8", "9");
+        filter.filterVersions(ctx);
+        assertVersions(ctx, "1");
+    }
+
+    @Test
+    void testDeriveChildFilter() {
+        LowestVersionFilter filter = new LowestVersionFilter();
+        assertSame(filter, derive(filter, "g:a:1"));
+    }
+
+    @SuppressWarnings("EqualsWithItself")
+    @Test
+    void testEquals() {
+        LowestVersionFilter filter = new LowestVersionFilter();
+        assertNotEquals(null, filter);
+        assertEquals(filter, filter);
+        assertEquals(filter, new LowestVersionFilter());
+    }
+}

maven-resolver-util/src/test/java/org/eclipse/aether/util/graph/versions/PredicateVersionFilterTest.java

@@ -0,0 +1,59 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.eclipse.aether.util.graph.versions;
+
+import java.util.function.Predicate;
+
+import org.eclipse.aether.artifact.Artifact;
+import org.eclipse.aether.collection.VersionFilter.VersionFilterContext;
+import org.eclipse.aether.util.graph.version.PredicateVersionFilter;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+public class PredicateVersionFilterTest extends AbstractVersionFilterTest {
+
+    @Test
+    void testFilterVersions() {
+        Predicate<Artifact> oddVersions = a -> Integer.parseInt(a.getVersion()) % 2 != 0;
+        PredicateVersionFilter filter = new PredicateVersionFilter(oddVersions);
+        VersionFilterContext ctx = newContext("g:a:[1,9]", "1", "2", "3", "4", "5", "6", "7", "8", "9");
+        filter.filterVersions(ctx);
+        assertVersions(ctx, "1", "3", "5", "7", "9");
+    }
+
+    @Test
+    void testDeriveChildFilter() {
+        PredicateVersionFilter filter = new PredicateVersionFilter(a -> true);
+        assertSame(filter, derive(filter, "g:a:1"));
+    }
+
+    @Test
+    void testEquals() {
+        Predicate<Artifact> falsePredicate = a -> false;
+        Predicate<Artifact> truePredicate = a -> true;
+        PredicateVersionFilter filter1 = new PredicateVersionFilter(falsePredicate);
+        PredicateVersionFilter filter2 = new PredicateVersionFilter(falsePredicate);
+        PredicateVersionFilter filter3 = new PredicateVersionFilter(truePredicate);
+        assertNotEquals(null, filter1);
+        assertEquals(filter1, filter2);
+        assertNotEquals(filter2, filter3);
+        assertEquals(filter1, new PredicateVersionFilter(falsePredicate));
+    }
+}