DependencyCollectionChecker: new session member

maven-resolver-api/src/main/java/org/eclipse/aether/AbstractForwardingRepositorySystemSession.java

@@ -21,6 +21,7 @@
 import java.util.Map;
 
 import org.eclipse.aether.artifact.ArtifactTypeRegistry;
+import org.eclipse.aether.collection.DependencyCollectionChecker;
 import org.eclipse.aether.collection.DependencyGraphTransformer;
 import org.eclipse.aether.collection.DependencyManager;
 import org.eclipse.aether.collection.DependencySelector;
@@ -198,6 +199,11 @@ public ScopeManager getScopeManager() {
         return getSession().getScopeManager();
     }
 
+    @Override
+    public DependencyCollectionChecker getDependencyCollectionChecker() {
+        return getSession().getDependencyCollectionChecker();
+    }
+
     @Override
     public SystemDependencyScope getSystemDependencyScope() {
         return getSession().getSystemDependencyScope();

maven-resolver-api/src/main/java/org/eclipse/aether/DefaultRepositorySystemSession.java

@@ -25,6 +25,7 @@
 
 import org.eclipse.aether.artifact.ArtifactType;
 import org.eclipse.aether.artifact.ArtifactTypeRegistry;
+import org.eclipse.aether.collection.DependencyCollectionChecker;
 import org.eclipse.aether.collection.DependencyGraphTransformer;
 import org.eclipse.aether.collection.DependencyManager;
 import org.eclipse.aether.collection.DependencySelector;
@@ -128,6 +129,8 @@ public final class DefaultRepositorySystemSession implements RepositorySystemSes
 
     private ScopeManager scopeManager;
 
+    private DependencyCollectionChecker dependencyCollectionChecker;
+
     private final Function<Runnable, Boolean> onSessionEndedRegistrar;
 
     /**
@@ -206,6 +209,7 @@ public DefaultRepositorySystemSession(RepositorySystemSession session) {
         setData(session.getData());
         setCache(session.getCache());
         setScopeManager(session.getScopeManager());
+        setDependencyCollectionChecker(session.getDependencyCollectionChecker());
         this.onSessionEndedRegistrar = session::addOnSessionEndedHandler;
     }
 
@@ -832,6 +836,24 @@ public SystemDependencyScope getSystemDependencyScope() {
         }
     }
 
+    @Override
+    public DependencyCollectionChecker getDependencyCollectionChecker() {
+        return dependencyCollectionChecker;
+    }
+
+    /**
+     * Sets the dependency collection checker, may be {@code null}.
+     *
+     * @param dependencyCollectionChecker The dependency collection checker, may be {@code null}.
+     * @return The session for chaining, never {@code null}.
+     * @since 2.0.19
+     */
+    public DefaultRepositorySystemSession setDependencyCollectionChecker(
+            DependencyCollectionChecker dependencyCollectionChecker) {
+        this.dependencyCollectionChecker = dependencyCollectionChecker;
+        return this;
+    }
+
     /**
      * Registers onSessionEnded handler, if able to.
      *

maven-resolver-api/src/main/java/org/eclipse/aether/RepositorySystemSession.java

@@ -25,6 +25,7 @@
 import java.util.function.Supplier;
 
 import org.eclipse.aether.artifact.ArtifactTypeRegistry;
+import org.eclipse.aether.collection.DependencyCollectionChecker;
 import org.eclipse.aether.collection.DependencyGraphTransformer;
 import org.eclipse.aether.collection.DependencyManager;
 import org.eclipse.aether.collection.DependencySelector;
@@ -405,6 +406,15 @@ interface SessionBuilder {
          */
         SessionBuilder setScopeManager(ScopeManager scopeManager);
 
+        /**
+         * Sets the dependency collection checker, may be {@code null}.
+         *
+         * @param dependencyCollectionChecker The checker instance, may be {@code null}.
+         * @return The session for chaining, may be {@code null}.
+         * @since 2.0.19
+         */
+        SessionBuilder setDependencyCollectionChecker(DependencyCollectionChecker dependencyCollectionChecker);
+
         /**
          * Adds on session ended handler to be immediately registered when this builder creates session.
          *
@@ -782,6 +792,14 @@ interface SessionBuilder {
      */
     SystemDependencyScope getSystemDependencyScope();
 
+    /**
+     * Returns the dependency collector checker, may be {@code null}.
+     *
+     * @return The effective {@link DependencyCollectionChecker} instance, may be {@code null}.
+     * @since 2.0.19
+     */
+    DependencyCollectionChecker getDependencyCollectionChecker();
+
     /**
      * Registers a handler to execute when this session closed.
      * <p>

maven-resolver-api/src/main/java/org/eclipse/aether/collection/DependencyCollectionChecker.java

@@ -0,0 +1,58 @@
+/*
+ * 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.collection;
+
+import org.eclipse.aether.RepositorySystemSession;
+
+/**
+ * Dependency collector checker. It is able to check dependency collection result, deem it "satisfiable" or
+ * augment collection and re-execute it.
+ *
+ * @since 2.0.19
+ */
+public interface DependencyCollectionChecker {
+    /**
+     * A default "no op" implementation.
+     */
+    DependencyCollectionChecker NOOP = new DependencyCollectionChecker() {};
+
+    /**
+     * Config property for collector checker suppression. Presence of this key will suppress collection checking.
+     * This key is not meant for users, but to programmatically signal collection suppression.
+     */
+    String COLLECTOR_CHECKER_SUPPRESSED = "aether.dependencyCollector.checker.suppressed";
+
+    /**
+     * Prepares for dependency collection.
+     */
+    default RepositorySystemSession prepare(RepositorySystemSession session, CollectRequest request) {
+        return session;
+    }
+
+    /**
+     * Performs checks on finished dependency collection. It should return {@code true} if the collection was deemed
+     * "satisfactory". If should return {@code false} <em>only, if collection was not satisfactory, and checker
+     * was able to modify resolution parameters (to not repeat same work)</em>. In other cases (not satisfactory
+     * but no param change would help) it should throw {@link DependencyCollectionException}.
+     */
+    default boolean isSatisfactory(RepositorySystemSession session, CollectRequest request, CollectResult result)
+            throws DependencyCollectionException {
+        return true;
+    }
+}