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/DefaultModelUrlNormalizer.java

@@ -52,26 +52,35 @@ public Model normalize(Model model, ModelBuilderRequest request) {
         }
 
         Model.Builder builder = Model.newBuilder(model);
-        builder.url(normalize(model.getUrl()));
+        normalizeBuilder(builder);
+        return builder.build();
+    }
+
+    @Override
+    public void normalize(Model.Builder builder, ModelBuilderRequest request) {
+        normalizeBuilder(builder);
+    }
+
+    private void normalizeBuilder(Model.Builder builder) {
+        builder.url(normalize(builder.getUrl()));
 
-        Scm scm = model.getScm();
+        Scm scm = builder.getScm();
         if (scm != null) {
-            builder.scm(Scm.newBuilder(scm)
+            builder.getModifiableScm()
                     .url(normalize(scm.getUrl()))
                     .connection(normalize(scm.getConnection()))
-                    .developerConnection(normalize(scm.getDeveloperConnection()))
-                    .build());
+                    .developerConnection(normalize(scm.getDeveloperConnection()));
         }
 
-        DistributionManagement dist = model.getDistributionManagement();
+        DistributionManagement dist = builder.getDistributionManagement();
         if (dist != null) {
             Site site = dist.getSite();
             if (site != null) {
-                builder.distributionManagement(dist.withSite(site.withUrl(normalize(site.getUrl()))));
+                builder.getModifiableDistributionManagement()
+                        .getModifiableSite()
+                        .url(normalize(site.getUrl()));
             }
         }
-
-        return builder.build();
     }
 
     private String normalize(String url) {

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

@@ -44,6 +44,26 @@
 @Singleton
 public class DefaultPluginConfigurationExpander implements PluginConfigurationExpander {
 
+    @Override
+    public void expandPluginConfiguration(
+            Model.Builder builder, ModelBuilderRequest request, ModelProblemCollector problems) {
+
+        // Mutate the Build sub-builder in place to avoid intermediate immutable allocations
+        Build build = builder.getBuild();
+        if (build != null) {
+            Build.Builder bb = builder.getModifiableBuild();
+            bb.plugins(expandPlugin(build.getPlugins()));
+            PluginManagement pluginManagement = build.getPluginManagement();
+            if (pluginManagement != null) {
+                bb.getModifiablePluginManagement().plugins(expandPlugin(pluginManagement.getPlugins()));
+            }
+        }
+        Reporting reporting = builder.getReporting();
+        if (reporting != null) {
+            expandReport(reporting.getPlugins());
+        }
+    }
+
     @Override
     public Model expandPluginConfiguration(Model model, ModelBuilderRequest request, ModelProblemCollector problems) {
         Build build = model.getBuild();