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

api/maven-api-core/src/main/java/org/apache/maven/api/services/xml/XmlReaderRequest.java

@@ -66,6 +66,20 @@ public interface XmlReaderRequest {
 
     boolean isAddDefaultEntities();
 
+    /**
+     * Indicates whether location information (line/column tracking) should be
+     * recorded during parsing. Defaults to {@code true}. Setting this to
+     * {@code false} for imported dependency management POMs avoids allocating
+     * location maps that are never read, significantly reducing memory churn
+     * in large reactors.
+     *
+     * @return {@code true} if location information should be tracked
+     * @since 4.0.0
+     */
+    default boolean isAddLocationInformation() {
+        return true;
+    }
+
     interface Transformer {
         /**
          * Interpolate the value read from the xml document
@@ -95,6 +109,7 @@ class XmlReaderRequestBuilder {
         String modelId;
         String location;
         boolean addDefaultEntities = true;
+        boolean addLocationInformation = true;
 
         public XmlReaderRequestBuilder path(Path path) {
             this.path = path;
@@ -146,6 +161,11 @@ public XmlReaderRequestBuilder addDefaultEntities(boolean addDefaultEntities) {
             return this;
         }
 
+        public XmlReaderRequestBuilder addLocationInformation(boolean addLocationInformation) {
+            this.addLocationInformation = addLocationInformation;
+            return this;
+        }
+
         public XmlReaderRequest build() {
             return new DefaultXmlReaderRequest(
                     path,
@@ -157,7 +177,8 @@ public XmlReaderRequest build() {
                     strict,
                     modelId,
                     location,
-                    addDefaultEntities);
+                    addDefaultEntities,
+                    addLocationInformation);
         }
 
         private static class DefaultXmlReaderRequest implements XmlReaderRequest {
@@ -171,6 +192,7 @@ private static class DefaultXmlReaderRequest implements XmlReaderRequest {
             final String modelId;
             final String location;
             final boolean addDefaultEntities;
+            final boolean addLocationInformation;
 
             @SuppressWarnings("checkstyle:ParameterNumber")
             DefaultXmlReaderRequest(
@@ -183,7 +205,8 @@ private static class DefaultXmlReaderRequest implements XmlReaderRequest {
                     boolean strict,
                     String modelId,
                     String location,
-                    boolean addDefaultEntities) {
+                    boolean addDefaultEntities,
+                    boolean addLocationInformation) {
                 this.path = path;
                 this.rootDirectory = rootDirectory;
                 this.url = url;
@@ -194,6 +217,7 @@ private static class DefaultXmlReaderRequest implements XmlReaderRequest {
                 this.modelId = modelId;
                 this.location = location;
                 this.addDefaultEntities = addDefaultEntities;
+                this.addLocationInformation = addLocationInformation;
             }
 
             @Override
@@ -245,6 +269,11 @@ public String getLocation() {
             public boolean isAddDefaultEntities() {
                 return addDefaultEntities;
             }
+
+            @Override
+            public boolean isAddLocationInformation() {
+                return addLocationInformation;
+            }
         }
     }
 }

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-core/src/main/java/org/apache/maven/graph/DefaultGraphBuilder.java

@@ -157,8 +157,7 @@ private List<MavenProject> trimProjectsToRequest(
         if (request.getPom() != null) {
             result = getProjectsInRequestScope(request, activeProjects);
 
-            List<MavenProject> sortedProjects = graph.getSortedProjects();
-            result.sort(comparing(sortedProjects::indexOf));
+            result.sort(comparing(buildProjectIndexMap(graph.getSortedProjects())::get));
 
             result = includeAlsoMakeTransitively(result, request, graph);
         }
@@ -189,8 +188,7 @@ private List<MavenProject> trimSelectedProjects(
                 result = includeAlsoMakeTransitively(result, request, graph);
 
                 // Order the new list in the original order
-                List<MavenProject> sortedProjects = graph.getSortedProjects();
-                result.sort(comparing(sortedProjects::indexOf));
+                result.sort(comparing(buildProjectIndexMap(graph.getSortedProjects())::get));
             }
         }
 
@@ -290,13 +288,24 @@ private List<MavenProject> includeAlsoMakeTransitively(
             result = new ArrayList<>(projectsSet);
 
             // Order the new list in the original order
-            List<MavenProject> sortedProjects = graph.getSortedProjects();
-            result.sort(comparing(sortedProjects::indexOf));
+            result.sort(comparing(buildProjectIndexMap(graph.getSortedProjects())::get));
         }
 
         return result;
     }
 
+    /**
+     * Builds a Map from MavenProject to its index in the sorted list, enabling O(1) index lookups
+     * for sorting instead of O(n) ArrayList.indexOf() scans that cause O(n² log n) sort performance.
+     */
+    private static Map<MavenProject, Integer> buildProjectIndexMap(List<MavenProject> sortedProjects) {
+        Map<MavenProject, Integer> indexMap = new HashMap<>(sortedProjects.size() * 2);
+        for (int i = 0; i < sortedProjects.size(); i++) {
+            indexMap.put(sortedProjects.get(i), i);
+        }
+        return indexMap;
+    }
+
     private void enrichRequestFromResumptionData(List<MavenProject> projects, MavenExecutionRequest request) {
         if (request.isResume()) {
             projects.stream()