Use Java 11 collections conveniences everywhere

modules/lang-mustache/src/main/java/org/elasticsearch/script/mustache/CustomMustacheFactory.java

@@ -30,6 +30,7 @@
 import com.github.mustachejava.codes.DefaultMustache;
 import com.github.mustachejava.codes.IterableCode;
 import com.github.mustachejava.codes.WriteCode;
+import org.apache.lucene.search.highlight.DefaultEncoder;
 import org.elasticsearch.common.Strings;
 import org.elasticsearch.common.xcontent.XContentBuilder;
 import org.elasticsearch.common.xcontent.XContentType;
@@ -86,11 +87,11 @@ public void encode(String value, Writer writer) {
     }
 
     static Encoder createEncoder(String mimeType) {
-        Supplier<Encoder> supplier = ENCODERS.get(mimeType);
+        final Supplier<Encoder> supplier = ENCODERS.get(mimeType);
         if (supplier == null) {
             throw new IllegalArgumentException("No encoder found for MIME type [" + mimeType + "]");
         }
-        return supplier.get();
+        return ENCODERS.get(mimeType).get();
     }
 
     @Override

modules/lang-mustache/src/test/java/org/elasticsearch/script/mustache/CustomMustacheFactoryTests.java

@@ -37,14 +37,22 @@
 public class CustomMustacheFactoryTests extends ESTestCase {
 
     public void testCreateEncoder() {
-        IllegalArgumentException e = expectThrows(IllegalArgumentException.class, () -> CustomMustacheFactory.createEncoder(null));
-        assertThat(e.getMessage(), equalTo("No encoder found for MIME type [null]"));
-
-        e = expectThrows(IllegalArgumentException.class, () -> CustomMustacheFactory.createEncoder(""));
-        assertThat(e.getMessage(), equalTo("No encoder found for MIME type []"));
-
-        e = expectThrows(IllegalArgumentException.class, () -> CustomMustacheFactory.createEncoder("test"));
-        assertThat(e.getMessage(), equalTo("No encoder found for MIME type [test]"));
+        {
+            final IllegalArgumentException e =
+                    expectThrows(IllegalArgumentException.class, () -> CustomMustacheFactory.createEncoder("non-existent"));
+            assertThat(e.getMessage(), equalTo("No encoder found for MIME type [non-existent]"));
+        }
+
+        {
+            final IllegalArgumentException e = expectThrows(IllegalArgumentException.class, () -> CustomMustacheFactory.createEncoder(""));
+            assertThat(e.getMessage(), equalTo("No encoder found for MIME type []"));
+        }
+
+        {
+            final IllegalArgumentException e =
+                    expectThrows(IllegalArgumentException.class, () -> CustomMustacheFactory.createEncoder("test"));
+            assertThat(e.getMessage(), equalTo("No encoder found for MIME type [test]"));
+        }
 
         assertThat(CustomMustacheFactory.createEncoder(CustomMustacheFactory.JSON_MIME_TYPE_WITH_CHARSET),
             instanceOf(CustomMustacheFactory.JsonEscapeEncoder.class));

server/src/main/java/org/elasticsearch/index/mapper/DocumentMapperParser.java

@@ -132,7 +132,8 @@ private DocumentMapper parse(String type, Map<String, Object> mapping, String de
              *
              * Note: this copy can not be replaced by Map#copyOf because we rely on consistent serialization order since we do byte-level
              * checks on the mapping between what we receive from the master and what we have locally. As Map#copyOf is not necessarily
-             * the same underlying map implementation, we could end up with a different iteration order.
+             * the same underlying map implementation, we could end up with a different iteration order. For reference, see
+             * MapperService#assertSerializtion and GitHub issues #10302 and #10318.
              *
              * Do not change this to Map#copyOf or any other method of copying meta that could change the iteration order.
              *

x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/utils/TypedChainTaskExecutor.java

@@ -63,7 +63,8 @@ private synchronized void execute(T previousValue, ActionListener<List<T>> liste
         collectedResponses.add(previousValue);
         if (continuationPredicate.test(previousValue)) {
             if (tasks.isEmpty()) {
-               listener.onResponse(List.copyOf(collectedResponses));
+                // noinspection Java9CollectionFactory (because the list can contain null entries)
+                listener.onResponse(Collections.unmodifiableList(new ArrayList<>(collectedResponses)));
                return;
             }
             ChainTask<T> task = tasks.pop();
@@ -83,7 +84,8 @@ protected void doRun() {
                 }
             });
         } else {
-            listener.onResponse(List.copyOf(collectedResponses));
+            // noinspection Java9CollectionFactory (because the list can contain null entries)
+            listener.onResponse(Collections.unmodifiableList(new ArrayList<>(collectedResponses)));
         }
     }