[3.9.x][MNG-8106] Fix metadata merge (#1480)

As currently if given metadata serves multiple roles (G, A or V level), data loss occurs.

---

https://issues.apache.org/jira/browse/MNG-8106

Author: cstamas

.github/workflows/maven.yml

@@ -43,7 +43,7 @@ jobs:
       - uses: actions/setup-java@v4
         with:
           java-version: 8
-          distribution: 'temurin'
+          distribution: 'zulu'
           cache: 'maven'
 
       - name: Build with Maven
@@ -125,7 +125,7 @@ jobs:
         uses: actions/setup-java@v4
         with:
           java-version: ${{ matrix.java }}
-          distribution: 'temurin'
+          distribution: 'zulu'
           cache: 'maven'
 
       - name: Running integration tests

maven-resolver-provider/src/main/java/org/apache/maven/repository/internal/LocalSnapshotMetadata.java

@@ -116,6 +116,10 @@ protected void merge(Metadata recessive) {
 
             metadata.getVersioning().setSnapshotVersions(new ArrayList<>(versions.values()));
         }
+        // just carry-on as-is
+        if (!recessive.getPlugins().isEmpty()) {
+            metadata.setPlugins(new ArrayList<>(recessive.getPlugins()));
+        }
 
         artifacts.clear();
     }

maven-resolver-provider/src/main/java/org/apache/maven/repository/internal/PluginsMetadata.java

@@ -74,12 +74,16 @@ private static Metadata createRepositoryMetadata(PluginInfo pluginInfo) {
     protected void merge(Metadata recessive) {
         List<Plugin> recessivePlugins = recessive.getPlugins();
         List<Plugin> plugins = metadata.getPlugins();
-        if (!plugins.isEmpty()) {
+        if (!recessivePlugins.isEmpty() || !plugins.isEmpty()) {
             LinkedHashMap<String, Plugin> mergedPlugins = new LinkedHashMap<>();
             recessivePlugins.forEach(p -> mergedPlugins.put(p.getPrefix(), p));
             plugins.forEach(p -> mergedPlugins.put(p.getPrefix(), p));
             metadata.setPlugins(new ArrayList<>(mergedPlugins.values()));
         }
+        // just carry-on as-is
+        if (recessive.getVersioning() != null) {
+            metadata.setVersioning(recessive.getVersioning());
+        }
     }
 
     @Override

maven-resolver-provider/src/main/java/org/apache/maven/repository/internal/RemoteSnapshotMetadata.java

@@ -124,6 +124,10 @@ protected void merge(Metadata recessive) {
         if (!legacyFormat) {
             metadata.getVersioning().setSnapshotVersions(new ArrayList<>(versions.values()));
         }
+        // just carry-on as-is
+        if (!recessive.getPlugins().isEmpty()) {
+            metadata.setPlugins(new ArrayList<>(recessive.getPlugins()));
+        }
     }
 
     private static int getBuildNumber(Metadata metadata) {

maven-resolver-provider/src/main/java/org/apache/maven/repository/internal/VersionsMetadata.java

@@ -83,6 +83,10 @@ protected void merge(Metadata recessive) {
             versions.addAll(versioning.getVersions());
             versioning.setVersions(new ArrayList<>(versions));
         }
+        // just carry-on as-is
+        if (!recessive.getPlugins().isEmpty()) {
+            metadata.setPlugins(new ArrayList<>(recessive.getPlugins()));
+        }
     }
 
     public Object getKey() {