This can just be BiFunction

We don't need a purpose-built interface for these.

Author: joegallo

x-pack/plugin/deprecation/src/main/java/org/elasticsearch/xpack/deprecation/DeprecationChecks.java

@@ -21,6 +21,7 @@
 import java.util.Collections;
 import java.util.List;
 import java.util.Objects;
+import java.util.function.BiFunction;
 import java.util.function.Function;
 import java.util.stream.Collectors;
 import java.util.stream.Stream;
@@ -138,7 +139,7 @@ private DeprecationChecks() {
             ).collect(Collectors.toList());
         }
 
-    static List<IndexDeprecationCheck<ClusterState, IndexMetadata, DeprecationIssue>> INDEX_SETTINGS_CHECKS =
+    static List<BiFunction<ClusterState, IndexMetadata, DeprecationIssue>> INDEX_SETTINGS_CHECKS =
         Collections.unmodifiableList(Arrays.asList(
             (clusterState, indexMetadata) -> IndexDeprecationChecks.oldIndicesCheck(indexMetadata),
             (clusterState, indexMetadata) -> IndexDeprecationChecks.tooManyFieldsCheck(indexMetadata),
@@ -175,9 +176,4 @@ static <T> List<DeprecationIssue> filterChecks(List<T> checks, Function<T, Depre
     public interface NodeDeprecationCheck<A, B, C, D, R> {
         R apply(A first, B second, C third, D fourth);
     }
-
-    @FunctionalInterface
-    public interface IndexDeprecationCheck<A, B, R> {
-        R apply(A first, B second);
-    }
 }

x-pack/plugin/deprecation/src/main/java/org/elasticsearch/xpack/deprecation/DeprecationInfoAction.java

@@ -39,6 +39,7 @@
 import java.util.Map;
 import java.util.Objects;
 import java.util.Set;
+import java.util.function.BiFunction;
 import java.util.function.Function;
 import java.util.stream.Collectors;
 
@@ -203,7 +204,7 @@ public static DeprecationInfoAction.Response from(
             IndexNameExpressionResolver indexNameExpressionResolver,
             Request request,
             NodesDeprecationCheckResponse nodeDeprecationResponse,
-            List<DeprecationChecks.IndexDeprecationCheck<ClusterState, IndexMetadata, DeprecationIssue>> indexSettingsChecks,
+            List<BiFunction<ClusterState, IndexMetadata, DeprecationIssue>> indexSettingsChecks,
             List<Function<ClusterState, DeprecationIssue>> clusterSettingsChecks,
             Map<String, List<DeprecationIssue>> pluginSettingIssues,
             List<String> skipTheseDeprecatedSettings

x-pack/plugin/deprecation/src/test/java/org/elasticsearch/xpack/deprecation/DeprecationInfoActionResponseTests.java

@@ -36,6 +36,7 @@
 import java.util.Map;
 import java.util.Set;
 import java.util.concurrent.atomic.AtomicReference;
+import java.util.function.BiFunction;
 import java.util.function.Function;
 import java.util.stream.Collectors;
 import java.util.stream.Stream;
@@ -97,7 +98,7 @@ public void testFrom() throws IOException {
             Collections.unmodifiableList(Arrays.asList(
                 (s) -> clusterIssueFound ? foundIssue : null
             ));
-        List<DeprecationChecks.IndexDeprecationCheck<ClusterState, IndexMetadata, DeprecationIssue>> indexSettingsChecks =
+        List<BiFunction<ClusterState, IndexMetadata, DeprecationIssue>> indexSettingsChecks =
             Collections.unmodifiableList(Arrays.asList(
                 (cs, idx) -> indexIssueFound ? foundIssue : null
             ));
@@ -170,7 +171,7 @@ public void testRemoveSkippedSettings() throws IOException {
                 }
             ));
         AtomicReference<Settings> visibleIndexSettings = new AtomicReference<>();
-        List<DeprecationChecks.IndexDeprecationCheck<ClusterState, IndexMetadata, DeprecationIssue>> indexSettingsChecks =
+        List<BiFunction<ClusterState, IndexMetadata, DeprecationIssue>> indexSettingsChecks =
             Collections.unmodifiableList(Arrays.asList(
                 (cs, idx) -> {
                     visibleIndexSettings.set(idx.getSettings());