Optimize model building pipeline: defer Dependency.build() and reduce allocations

api/maven-api-spi/src/main/java/org/apache/maven/api/services/model/DependencyManagementImporter.java

@@ -45,4 +45,21 @@ Model importManagement(
             List<? extends DependencyManagement> sources,
             ModelBuilderRequest request,
             ModelProblemCollector problems);
+
+    /**
+     * Builder-accepting variant of {@link #importManagement}.
+     *
+     * @since 4.0.0
+     */
+    default void importManagement(
+            Model.Builder builder,
+            List<? extends DependencyManagement> sources,
+            ModelBuilderRequest request,
+            ModelProblemCollector problems) {
+        Model built = builder.build();
+        Model result = importManagement(built, sources, request, problems);
+        if (result != built) {
+            builder.reset(result);
+        }
+    }
 }

api/maven-api-spi/src/main/java/org/apache/maven/api/services/model/DependencyManagementInjector.java

@@ -38,4 +38,24 @@ public interface DependencyManagementInjector {
      * @param problems The container used to collect problems that were encountered, must not be {@code null}.
      */
     Model injectManagement(Model model, ModelBuilderRequest request, ModelProblemCollector problems);
+
+    /**
+     * Builder-accepting variant that operates on a {@link Model.Builder} directly,
+     * avoiding an intermediate {@code Model.build()} between pipeline stages.
+     * <p>
+     * The default implementation bridges to {@link #injectManagement(Model, ModelBuilderRequest, ModelProblemCollector)}
+     * by building the model, processing it, and resetting the builder to the result.
+     *
+     * @param builder The model builder to modify in place, must not be {@code null}.
+     * @param request The model building request, must not be {@code null}.
+     * @param problems The container used to collect problems, must not be {@code null}.
+     * @since 4.0.0
+     */
+    default void injectManagement(Model.Builder builder, ModelBuilderRequest request, ModelProblemCollector problems) {
+        Model built = builder.build();
+        Model result = injectManagement(built, request, problems);
+        if (result != built) {
+            builder.reset(result);
+        }
+    }
 }

api/maven-api-spi/src/main/java/org/apache/maven/api/services/model/InheritanceAssembler.java

@@ -42,4 +42,18 @@ public interface InheritanceAssembler {
      */
     Model assembleModelInheritance(
             Model child, Model parent, ModelBuilderRequest request, ModelProblemCollector problems);
+
+    /**
+     * Builder-accepting variant that merges parent values into the child builder directly.
+     *
+     * @since 4.0.0
+     */
+    default void assembleModelInheritance(
+            Model.Builder childBuilder, Model parent, ModelBuilderRequest request, ModelProblemCollector problems) {
+        Model built = childBuilder.build();
+        Model result = assembleModelInheritance(built, parent, request, problems);
+        if (result != built) {
+            childBuilder.reset(result);
+        }
+    }
 }

api/maven-api-spi/src/main/java/org/apache/maven/api/services/model/ModelInterpolator.java

@@ -51,4 +51,21 @@ Model interpolateModel(
             @Nullable Path projectDir,
             @Nonnull ModelBuilderRequest request,
             @Nonnull ModelProblemCollector problems);
+
+    /**
+     * Builder-accepting variant of {@link #interpolateModel}.
+     *
+     * @since 4.0.0
+     */
+    default void interpolateModel(
+            @Nonnull Model.Builder builder,
+            @Nullable Path projectDir,
+            @Nonnull ModelBuilderRequest request,
+            @Nonnull ModelProblemCollector problems) {
+        Model built = builder.build();
+        Model result = interpolateModel(built, projectDir, request, problems);
+        if (result != built) {
+            builder.reset(result);
+        }
+    }
 }

api/maven-api-spi/src/main/java/org/apache/maven/api/services/model/ModelNormalizer.java

@@ -48,4 +48,31 @@ public interface ModelNormalizer {
      * @param problems The container used to collect problems that were encountered, must not be {@code null}.
      */
     Model injectDefaultValues(Model model, ModelBuilderRequest request, ModelProblemCollector problems);
+
+    /**
+     * Builder-accepting variant of {@link #mergeDuplicates}.
+     *
+     * @since 4.0.0
+     */
+    default void mergeDuplicates(Model.Builder builder, ModelBuilderRequest request, ModelProblemCollector problems) {
+        Model built = builder.build();
+        Model result = mergeDuplicates(built, request, problems);
+        if (result != built) {
+            builder.reset(result);
+        }
+    }
+
+    /**
+     * Builder-accepting variant of {@link #injectDefaultValues}.
+     *
+     * @since 4.0.0
+     */
+    default void injectDefaultValues(
+            Model.Builder builder, ModelBuilderRequest request, ModelProblemCollector problems) {
+        Model built = builder.build();
+        Model result = injectDefaultValues(built, request, problems);
+        if (result != built) {
+            builder.reset(result);
+        }
+    }
 }

api/maven-api-spi/src/main/java/org/apache/maven/api/services/model/ModelPathTranslator.java

@@ -40,4 +40,17 @@ public interface ModelPathTranslator {
      * @since 4.0.0
      */
     Model alignToBaseDirectory(Model model, Path basedir, ModelBuilderRequest request);
+
+    /**
+     * Builder-accepting variant of {@link #alignToBaseDirectory}.
+     *
+     * @since 4.0.0
+     */
+    default void alignToBaseDirectory(Model.Builder builder, Path basedir, ModelBuilderRequest request) {
+        Model built = builder.build();
+        Model result = alignToBaseDirectory(built, basedir, request);
+        if (result != built) {
+            builder.reset(result);
+        }
+    }
 }

api/maven-api-spi/src/main/java/org/apache/maven/api/services/model/ModelUrlNormalizer.java

@@ -36,4 +36,17 @@ public interface ModelUrlNormalizer {
      * @param request The model building request that holds further settings, must not be {@code null}.
      */
     Model normalize(Model model, ModelBuilderRequest request);
+
+    /**
+     * Builder-accepting variant of {@link #normalize}.
+     *
+     * @since 4.0.0
+     */
+    default void normalize(Model.Builder builder, ModelBuilderRequest request) {
+        Model built = builder.build();
+        Model result = normalize(built, request);
+        if (result != built) {
+            builder.reset(result);
+        }
+    }
 }

api/maven-api-spi/src/main/java/org/apache/maven/api/services/model/PluginConfigurationExpander.java

@@ -37,4 +37,18 @@ public interface PluginConfigurationExpander {
      * @param problems The container used to collect problems that were encountered, must not be {@code null}.
      */
     Model expandPluginConfiguration(Model model, ModelBuilderRequest request, ModelProblemCollector problems);
+
+    /**
+     * Builder-accepting variant of {@link #expandPluginConfiguration}.
+     *
+     * @since 4.0.0
+     */
+    default void expandPluginConfiguration(
+            Model.Builder builder, ModelBuilderRequest request, ModelProblemCollector problems) {
+        Model built = builder.build();
+        Model result = expandPluginConfiguration(built, request, problems);
+        if (result != built) {
+            builder.reset(result);
+        }
+    }
 }

api/maven-api-spi/src/main/java/org/apache/maven/api/services/model/PluginManagementInjector.java

@@ -38,4 +38,17 @@ public interface PluginManagementInjector {
      * @param problems The container used to collect problems that were encountered, must not be {@code null}.
      */
     Model injectManagement(Model model, ModelBuilderRequest request, ModelProblemCollector problems);
+
+    /**
+     * Builder-accepting variant of {@link #injectManagement}.
+     *
+     * @since 4.0.0
+     */
+    default void injectManagement(Model.Builder builder, ModelBuilderRequest request, ModelProblemCollector problems) {
+        Model built = builder.build();
+        Model result = injectManagement(built, request, problems);
+        if (result != built) {
+            builder.reset(result);
+        }
+    }
 }

api/maven-api-spi/src/main/java/org/apache/maven/api/services/model/ProfileInjector.java

@@ -57,4 +57,21 @@ default Model injectProfile(
      */
     Model injectProfiles(
             Model model, List<Profile> profiles, ModelBuilderRequest request, ModelProblemCollector problems);
+
+    /**
+     * Builder-accepting variant that injects profile values into the model builder directly.
+     *
+     * @since 4.0.0
+     */
+    default void injectProfiles(
+            Model.Builder builder,
+            List<Profile> profiles,
+            ModelBuilderRequest request,
+            ModelProblemCollector problems) {
+        Model built = builder.build();
+        Model result = injectProfiles(built, profiles, request, problems);
+        if (result != built) {
+            builder.reset(result);
+        }
+    }
 }

compat/maven-model-builder/src/test/java/org/apache/maven/model/building/FileToRawModelMergerTest.java

@@ -40,6 +40,10 @@ class FileToRawModelMergerTest {
     void testOverriddenMergeMethods() {
         List<String> methodNames = Stream.of(MavenMerger.class.getDeclaredMethods())
                 .filter(m -> m.getName().startsWith("merge"))
+                // Exclude *ToBuilder variants and void methods whose first parameter
+                // is a Builder — only the object-returning merge methods need overriding
+                .filter(m -> !m.getName().endsWith("ToBuilder"))
+                .filter(m -> !m.getParameterTypes()[0].getSimpleName().equals("Builder"))
                 .filter(m -> {
                     String baseName = m.getName().substring(5 /* merge */);
                     String entity = baseName.substring(baseName.indexOf('_') + 1);

impl/maven-impl/src/main/java/org/apache/maven/impl/DefaultPluginConfigurationExpander.java

@@ -44,6 +44,30 @@
 @Singleton
 public class DefaultPluginConfigurationExpander implements PluginConfigurationExpander {
 
+    @Override
+    public void expandPluginConfiguration(
+            Model.Builder builder, ModelBuilderRequest request, ModelProblemCollector problems) {
+
+        // Use builder getters instead of builder.build() to avoid materializing
+        // all model-object lists (especially dependencies) just to read Build/Reporting
+        Build build = builder.getBuild();
+        if (build != null) {
+            Build newBuild = build.withPlugins(expandPlugin(build.getPlugins()));
+            PluginManagement pluginManagement = newBuild.getPluginManagement();
+            if (pluginManagement != null) {
+                newBuild = newBuild.withPluginManagement(
+                        pluginManagement.withPlugins(expandPlugin(pluginManagement.getPlugins())));
+            }
+            if (newBuild != build) {
+                builder.build(newBuild);
+            }
+        }
+        Reporting reporting = builder.getReporting();
+        if (reporting != null) {
+            expandReport(reporting.getPlugins());
+        }
+    }
+
     @Override
     public Model expandPluginConfiguration(Model model, ModelBuilderRequest request, ModelProblemCollector problems) {
         Build build = model.getBuild();

impl/maven-impl/src/main/java/org/apache/maven/impl/model/DefaultDependencyManagementImporter.java

@@ -167,6 +167,8 @@ static Dependency updateWithImportedFrom(Dependency dependency, DependencyManage
         if (dependencySource == null
                 || bomSource == null
                 || Objects.equals(dependencySource.getModelId(), bomSource.getModelId())) {
+            // Use forceCopy=true since we only set importedFrom (no field changes that would
+            // trigger copy-on-write), and build immediately as we need the immutable result.
             return Dependency.newBuilder(dependency, true)
                     .importedFrom(bomLocation)
                     .build();

impl/maven-impl/src/main/java/org/apache/maven/impl/model/DefaultDependencyManagementInjector.java

@@ -45,6 +45,20 @@ public class DefaultDependencyManagementInjector implements DependencyManagement
 
     private ManagementModelMerger merger = new ManagementModelMerger();
 
+    @Override
+    public void injectManagement(Model.Builder builder, ModelBuilderRequest request, ModelProblemCollector problems) {
+        // Use builder getters instead of builder.build() to avoid materializing
+        // all model-object lists just to read Dependencies and DependencyManagement
+        DependencyManagement depMgmt = builder.getDependencyManagement();
+        if (depMgmt != null) {
+            List<Dependency> deps = builder.getBuiltDependencies();
+            List<Dependency> merged = merger.computeMergedDependencies(deps, depMgmt);
+            if (merged != null) {
+                builder.dependencies(merged);
+            }
+        }
+    }
+
     @Override
     public Model injectManagement(Model model, ModelBuilderRequest request, ModelProblemCollector problems) {
         return merger.mergeManagedDependencies(model);
@@ -55,41 +69,60 @@ public Model injectManagement(Model model, ModelBuilderRequest request, ModelPro
      */
     protected static class ManagementModelMerger extends MavenModelMerger {
 
-        public Model mergeManagedDependencies(Model model) {
+        /**
+         * Computes the merged dependency list, or returns {@code null} if no dependencies were modified.
+         */
+        List<Dependency> computeMergedDependencies(Model model) {
             DependencyManagement dependencyManagement = model.getDependencyManagement();
             if (dependencyManagement != null) {
-                Map<Object, Dependency> dependencies = new HashMap<>();
-                Map<Object, Object> context = Collections.emptyMap();
+                return computeMergedDependencies(model.getDependencies(), dependencyManagement);
+            }
+            return null;
+        }
 
-                for (Dependency dependency : model.getDependencies()) {
-                    Object key = getDependencyKey().apply(dependency);
-                    dependencies.put(key, dependency);
-                }
+        /**
+         * Computes the merged dependency list from pre-extracted deps and dep management,
+         * or returns {@code null} if no dependencies were modified.
+         */
+        List<Dependency> computeMergedDependencies(
+                List<Dependency> dependencies, DependencyManagement dependencyManagement) {
+            Map<Object, Dependency> originalDeps = new HashMap<>();
+            Map<Object, Dependency.Builder> builderDeps = new HashMap<>();
+            Map<Object, Object> context = Collections.emptyMap();
+
+            for (Dependency dependency : dependencies) {
+                Object key = getDependencyKey().apply(dependency);
+                originalDeps.put(key, dependency);
+            }
 
-                boolean modified = false;
-                for (Dependency managedDependency : dependencyManagement.getDependencies()) {
-                    Object key = getDependencyKey().apply(managedDependency);
-                    Dependency dependency = dependencies.get(key);
-                    if (dependency != null) {
-                        Dependency merged = mergeDependency(dependency, managedDependency, false, context);
-                        if (merged != dependency) {
-                            dependencies.put(key, merged);
-                            modified = true;
-                        }
+            boolean modified = false;
+            for (Dependency managedDependency : dependencyManagement.getDependencies()) {
+                Object key = getDependencyKey().apply(managedDependency);
+                Dependency dependency = originalDeps.get(key);
+                if (dependency != null) {
+                    Dependency.Builder merged = mergeDependencyToBuilder(dependency, managedDependency, false, context);
+                    if (merged != null) {
+                        builderDeps.put(key, merged);
+                        modified = true;
                     }
                 }
+            }
 
-                if (modified) {
-                    List<Dependency> newDeps = new ArrayList<>(dependencies.size());
-                    for (Dependency dep : model.getDependencies()) {
-                        Object key = getDependencyKey().apply(dep);
-                        Dependency dependency = dependencies.get(key);
-                        newDeps.add(dependency);
-                    }
-                    return Model.newBuilder(model).dependencies(newDeps).build();
+            if (modified) {
+                List<Dependency> newDeps = new ArrayList<>(originalDeps.size());
+                for (Dependency dep : dependencies) {
+                    Object key = getDependencyKey().apply(dep);
+                    Dependency.Builder builder = builderDeps.get(key);
+                    newDeps.add(builder != null ? builder.build() : dep);
                 }
+                return newDeps;
             }
-            return model;
+            return null;
+        }
+
+        public Model mergeManagedDependencies(Model model) {
+            List<Dependency> merged = computeMergedDependencies(model);
+            return merged != null ? Model.newBuilder(model).dependencies(merged).build() : model;
         }
 
         @Override