Fix PluginInfo bwc for opensearch_version field (#12543)

* Fix PluginInfo bwc for opensearch_version field

Signed-off-by: Abhilasha Seth <abseth@amazon.com>

* Update how empty range list is handled

Signed-off-by: Abhilasha Seth <abseth@amazon.com>

---------

Signed-off-by: Abhilasha Seth <abseth@amazon.com>
(cherry picked from commit a702f6a)
Signed-off-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

server/src/main/java/org/opensearch/plugins/PluginInfo.java

@@ -450,7 +450,7 @@ public List<SemverRange> getOpenSearchVersionRanges() {
      */
     public String getOpenSearchVersionRangesString() {
         if (opensearchVersionRanges == null || opensearchVersionRanges.isEmpty()) {
-            return "";
+            throw new IllegalStateException("Opensearch version ranges list cannot be empty");
         }
         if (opensearchVersionRanges.size() == 1) {
             return opensearchVersionRanges.get(0).toString();
@@ -491,7 +491,7 @@ public XContentBuilder toXContent(XContentBuilder builder, Params params) throws
         {
             builder.field("name", name);
             builder.field("version", version);
-            builder.field("opensearch_version", opensearchVersionRanges);
+            builder.field("opensearch_version", getOpenSearchVersionRangesString());
             builder.field("java_version", javaVersion);
             builder.field("description", description);
             builder.field("classname", classname);

server/src/test/java/org/opensearch/plugins/PluginInfoTests.java

@@ -37,7 +37,10 @@
 import org.opensearch.Version;
 import org.opensearch.action.admin.cluster.node.info.PluginsAndModules;
 import org.opensearch.common.io.stream.BytesStreamOutput;
+import org.opensearch.common.xcontent.json.JsonXContent;
 import org.opensearch.core.common.io.stream.ByteBufferStreamInput;
+import org.opensearch.core.xcontent.ToXContent;
+import org.opensearch.core.xcontent.XContentBuilder;
 import org.opensearch.semver.SemverRange;
 import org.opensearch.test.OpenSearchTestCase;
 
@@ -367,6 +370,31 @@ public void testSerialize() throws Exception {
         assertThat(info2.toString(), equalTo(info.toString()));
     }
 
+    public void testToXContent() throws Exception {
+        PluginInfo info = new PluginInfo(
+            "fake",
+            "foo",
+            "dummy",
+            Version.CURRENT,
+            "1.8",
+            "dummyClass",
+            "folder",
+            Collections.emptyList(),
+            false
+        );
+        XContentBuilder builder = JsonXContent.contentBuilder().prettyPrint();
+        String prettyPrint = info.toXContent(builder, ToXContent.EMPTY_PARAMS).prettyPrint().toString();
+        assertTrue(prettyPrint.contains("\"name\" : \"fake\""));
+        assertTrue(prettyPrint.contains("\"version\" : \"dummy\""));
+        assertTrue(prettyPrint.contains("\"opensearch_version\" : \"" + Version.CURRENT));
+        assertTrue(prettyPrint.contains("\"java_version\" : \"1.8\""));
+        assertTrue(prettyPrint.contains("\"description\" : \"foo\""));
+        assertTrue(prettyPrint.contains("\"classname\" : \"dummyClass\""));
+        assertTrue(prettyPrint.contains("\"custom_foldername\" : \"folder\""));
+        assertTrue(prettyPrint.contains("\"extended_plugins\" : [ ]"));
+        assertTrue(prettyPrint.contains("\"has_native_controller\" : false"));
+    }
+
     public void testPluginListSorted() {
         List<PluginInfo> plugins = new ArrayList<>();
         plugins.add(new PluginInfo("c", "foo", "dummy", Version.CURRENT, "1.8", "dummyclass", Collections.emptyList(), randomBoolean()));