Feat: Add id attribute (gav) support to Dependency, Exclusion, Mixin

api/maven-api-model/src/main/mdo/maven.mdo

@@ -1204,6 +1204,20 @@
         ]]>
       </description>
       <fields>
+        <field xml.attribute="true">
+          <name>id</name>
+          <version>4.2.0+</version>
+          <description>
+            <![CDATA[
+            Combined coordinates as {@code groupId:artifactId:version}.
+            When specified, it is split into the {@code groupId}, {@code artifactId},
+            and {@code version} fields during model normalization.
+            The individual child elements should not be specified when using this attribute.
+            @since Maven 4.2
+            ]]>
+          </description>
+          <type>String</type>
+        </field>
         <field>
           <name>groupId</name>
           <version>3.0.0+</version>
@@ -1440,6 +1454,20 @@
         ]]>
       </description>
       <fields>
+        <field xml.attribute="true">
+          <name>id</name>
+          <version>4.2.0+</version>
+          <description>
+            <![CDATA[
+            Combined coordinates as {@code groupId:artifactId}.
+            When specified, it is split into the {@code groupId} and {@code artifactId}
+            fields during model normalization.
+            The individual child elements should not be specified when using this attribute.
+            @since Maven 4.2
+            ]]>
+          </description>
+          <type>String</type>
+        </field>
         <field>
           <name>groupId</name>
           <version>4.0.0+</version>
@@ -1863,6 +1891,20 @@
         <version>4.1.0+</version>
         <superClass>Parent</superClass>
         <fields>
+            <field xml.attribute="true" xml.tagName="id">
+                <name>gav</name>
+                <version>4.2.0+</version>
+                <description>
+                    <![CDATA[
+                    Combined coordinates as {@code groupId:artifactId:version}.
+                    When specified, it is split into the {@code groupId}, {@code artifactId},
+                    and {@code version} fields during model normalization.
+                    The individual child elements should not be specified when using this attribute.
+                    @since Maven 4.2
+                    ]]>
+                </description>
+                <type>String</type>
+            </field>
             <field>
                 <name>classifier</name>
                 <version>4.1.0+</version>

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

@@ -29,6 +29,8 @@
 import org.apache.maven.api.di.Singleton;
 import org.apache.maven.api.model.Build;
 import org.apache.maven.api.model.Dependency;
+import org.apache.maven.api.model.Exclusion;
+import org.apache.maven.api.model.Mixin;
 import org.apache.maven.api.model.Model;
 import org.apache.maven.api.model.Plugin;
 import org.apache.maven.api.services.ModelBuilderRequest;
@@ -49,6 +51,9 @@ public class DefaultModelNormalizer implements ModelNormalizer {
     public Model mergeDuplicates(Model model, ModelBuilderRequest request, ModelProblemCollector problems) {
         Model.Builder builder = Model.newBuilder(model);
 
+        // Expand id attributes on mixins
+        builder.mixins(injectList(model.getMixins(), this::expandMixinGav));
+
         Build build = model.getBuild();
         if (build != null) {
             List<Plugin> plugins = build.getPlugins();
@@ -76,15 +81,20 @@ public Model mergeDuplicates(Model model, ModelBuilderRequest request, ModelProb
          * the way 2.x works. When we're in strict mode, the removal of duplicates just saves other merging steps from
          * aftereffects and bogus error messages.
          */
+        // Expand id attributes on dependencies (and their exclusions), then deduplicate
         List<Dependency> dependencies = model.getDependencies();
-        Map<String, Dependency> normalized = new LinkedHashMap<>(dependencies.size() * 2);
+        List<Dependency> expanded = injectList(dependencies, this::expandDependencyId);
+        if (expanded != null) {
+            dependencies = expanded;
+        }
 
+        Map<String, Dependency> normalizedDeps = new LinkedHashMap<>(dependencies.size() * 2);
         for (Dependency dependency : dependencies) {
-            normalized.put(dependency.getManagementKey(), dependency);
+            normalizedDeps.put(dependency.getManagementKey(), dependency);
         }
 
-        if (dependencies.size() != normalized.size()) {
-            builder.dependencies(normalized.values());
+        if (expanded != null || dependencies.size() != normalizedDeps.size()) {
+            builder.dependencies(normalizedDeps.values());
         }
 
         return builder.build();
@@ -144,4 +154,92 @@ private <T> List<T> injectList(List<T> list, UnaryOperator<T> modifer) {
         }
         return newList;
     }
+
+    /**
+     * Expands the {@code id} attribute on a dependency into its component fields.
+     * The id format is {@code groupId:artifactId:version}.
+     */
+    Dependency expandDependencyId(Dependency d) {
+        String id = d.getId();
+        if (id == null || id.isEmpty()) {
+            // No id attribute, but still expand exclusion ids
+            List<Exclusion> expanded = injectList(d.getExclusions(), this::expandExclusionId);
+            return expanded != null ? d.withExclusions(expanded) : d;
+        }
+        String[] parts = id.split(":");
+        if (parts.length != 3) {
+            // Invalid format — will be caught by the validator
+            return d;
+        }
+        Dependency.Builder builder = Dependency.newBuilder(d);
+        if (isBlank(d.getGroupId())) {
+            builder.groupId(parts[0]);
+        }
+        if (isBlank(d.getArtifactId())) {
+            builder.artifactId(parts[1]);
+        }
+        if (isBlank(d.getVersion())) {
+            builder.version(parts[2]);
+        }
+        List<Exclusion> expanded = injectList(d.getExclusions(), this::expandExclusionId);
+        if (expanded != null) {
+            builder.exclusions(expanded);
+        }
+        return builder.build();
+    }
+
+    /**
+     * Expands the {@code id} attribute on an exclusion into its component fields.
+     * The id format is {@code groupId:artifactId}.
+     */
+    Exclusion expandExclusionId(Exclusion e) {
+        String id = e.getId();
+        if (id == null || id.isEmpty()) {
+            return e;
+        }
+        String[] parts = id.split(":");
+        if (parts.length != 2) {
+            // Invalid format — will be caught by the validator
+            return e;
+        }
+        Exclusion.Builder builder = Exclusion.newBuilder(e);
+        if (isBlank(e.getGroupId())) {
+            builder.groupId(parts[0]);
+        }
+        if (isBlank(e.getArtifactId())) {
+            builder.artifactId(parts[1]);
+        }
+        return builder.build();
+    }
+
+    /**
+     * Expands the {@code id} (XML attribute) / {@code gav} (Java field) on a mixin
+     * into its component fields. The format is {@code groupId:artifactId:version}.
+     */
+    Mixin expandMixinGav(Mixin m) {
+        String gav = m.getGav();
+        if (gav == null || gav.isEmpty()) {
+            return m;
+        }
+        String[] parts = gav.split(":");
+        if (parts.length != 3) {
+            // Invalid format — will be caught by the validator
+            return m;
+        }
+        Mixin.Builder builder = Mixin.newBuilder(m);
+        if (isBlank(m.getGroupId())) {
+            builder.groupId(parts[0]);
+        }
+        if (isBlank(m.getArtifactId())) {
+            builder.artifactId(parts[1]);
+        }
+        if (isBlank(m.getVersion())) {
+            builder.version(parts[2]);
+        }
+        return builder.build();
+    }
+
+    private static boolean isBlank(String s) {
+        return s == null || s.isEmpty();
+    }
 }

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

@@ -237,7 +237,8 @@ private static boolean objectsEqual(Object obj1, Object obj2) {
          */
         private static boolean dependenciesEqual(
                 org.apache.maven.api.model.Dependency dep1, org.apache.maven.api.model.Dependency dep2) {
-            return Objects.equals(dep1.getGroupId(), dep2.getGroupId())
+            return Objects.equals(dep1.getId(), dep2.getId())
+                    && Objects.equals(dep1.getGroupId(), dep2.getGroupId())
                     && Objects.equals(dep1.getArtifactId(), dep2.getArtifactId())
                     && Objects.equals(dep1.getVersion(), dep2.getVersion())
                     && Objects.equals(dep1.getType(), dep2.getType())
@@ -286,6 +287,7 @@ private static int computeHashCode(Object obj) {
          */
         private static int dependencyHashCode(org.apache.maven.api.model.Dependency dep) {
             return Objects.hash(
+                    dep.getId(),
                     dep.getGroupId(),
                     dep.getArtifactId(),
                     dep.getVersion(),