Avoid extra allocations in RestGetAliasesAction

When no explicit aliases are provided in the call there is no need
to collect the index names or aliases into HashSets if they won't be
used.

Also fixed where the index name was being added for each loop of the
alias list.

Author: JeremyDahlgren

server/src/main/java/org/elasticsearch/rest/action/admin/indices/RestGetAliasesAction.java

@@ -76,27 +76,29 @@ public String getName() {
     }
 
     static RestResponse buildRestResponse(
-        boolean aliasesExplicitlyRequested,
         String[] requestedAliases,
         Map<String, List<AliasMetadata>> responseAliasMap,
         Map<String, List<DataStreamAlias>> dataStreamAliases,
         XContentBuilder builder
     ) throws Exception {
         final Set<String> indicesToDisplay = new HashSet<>();
         final Set<String> returnedAliasNames = new HashSet<>();
-        for (final Map.Entry<String, List<AliasMetadata>> cursor : responseAliasMap.entrySet()) {
-            for (final AliasMetadata aliasMetadata : cursor.getValue()) {
-                if (aliasesExplicitlyRequested) {
-                    // only display indices that have aliases
-                    indicesToDisplay.add(cursor.getKey());
+        final var aliasesExplicitlyRequested = requestedAliases.length > 0;
+
+        if (aliasesExplicitlyRequested) {
+            for (final Map.Entry<String, List<AliasMetadata>> cursor : responseAliasMap.entrySet()) {
+                // only display indices that have aliases
+                indicesToDisplay.add(cursor.getKey());
+                for (final AliasMetadata aliasMetadata : cursor.getValue()) {
+                    returnedAliasNames.add(aliasMetadata.alias());
                 }
-                returnedAliasNames.add(aliasMetadata.alias());
             }
+
+            dataStreamAliases.entrySet()
+                .stream()
+                .flatMap(entry -> entry.getValue().stream())
+                .forEach(dataStreamAlias -> returnedAliasNames.add(dataStreamAlias.getName()));
         }
-        dataStreamAliases.entrySet()
-            .stream()
-            .flatMap(entry -> entry.getValue().stream())
-            .forEach(dataStreamAlias -> returnedAliasNames.add(dataStreamAlias.getName()));
 
         // compute explicitly requested aliases that have are not returned in the result
         final SortedSet<String> missingAliases = new TreeSet<>();
@@ -206,7 +208,6 @@ public RestChannelConsumer prepareRequest(final RestRequest request, final NodeC
         // We can't remove this logic yet to support mixed clusters. We should be able to remove this logic here
         // in when 8.0 becomes the new version in the master branch.
 
-        final boolean namesProvided = request.hasParam("name");
         final String[] aliases = request.paramAsStringArrayOrEmptyIfAll("name");
         final var masterNodeTimeout = RestUtils.getMasterNodeTimeout(request);
         final GetAliasesRequest getAliasesRequest = new GetAliasesRequest(masterNodeTimeout, aliases);
@@ -234,7 +235,7 @@ public RestChannelConsumer prepareRequest(final RestRequest request, final NodeC
             .getAliases(getAliasesRequest, new RestBuilderListener<>(channel) {
                 @Override
                 public RestResponse buildResponse(GetAliasesResponse response, XContentBuilder builder) throws Exception {
-                    return buildRestResponse(namesProvided, aliases, response.getAliases(), response.getDataStreamAliases(), builder);
+                    return buildRestResponse(aliases, response.getAliases(), response.getDataStreamAliases(), builder);
                 }
             });
     }

server/src/test/java/org/elasticsearch/rest/action/admin/indices/RestGetAliasesActionTests.java

@@ -40,7 +40,6 @@ public void testBareRequest() throws Exception {
         final AliasMetadata foobarAliasMetadata = AliasMetadata.builder("foobar").build();
         final AliasMetadata fooAliasMetadata = AliasMetadata.builder("foo").build();
         final RestResponse restResponse = RestGetAliasesAction.buildRestResponse(
-            false,
             new String[0],
             Map.of("index", Arrays.asList(fooAliasMetadata, foobarAliasMetadata)),
             Map.of(),
@@ -54,7 +53,6 @@ public void testBareRequest() throws Exception {
     public void testSimpleAliasWildcardMatchingNothing() throws Exception {
         final XContentBuilder xContentBuilder = XContentFactory.contentBuilder(XContentType.JSON);
         final RestResponse restResponse = RestGetAliasesAction.buildRestResponse(
-            true,
             new String[] { "baz*" },
             Map.of(),
             Map.of(),
@@ -69,7 +67,6 @@ public void testMultipleAliasWildcardsSomeMatching() throws Exception {
         final XContentBuilder xContentBuilder = XContentFactory.contentBuilder(XContentType.JSON);
         final AliasMetadata aliasMetadata = AliasMetadata.builder("foobar").build();
         final RestResponse restResponse = RestGetAliasesAction.buildRestResponse(
-            true,
             new String[] { "baz*", "foobar*" },
             Map.of("index", List.of(aliasMetadata)),
             Map.of(),
@@ -83,7 +80,6 @@ public void testMultipleAliasWildcardsSomeMatching() throws Exception {
     public void testAliasWildcardsIncludeAndExcludeAll() throws Exception {
         final XContentBuilder xContentBuilder = XContentFactory.contentBuilder(XContentType.JSON);
         final RestResponse restResponse = RestGetAliasesAction.buildRestResponse(
-            true,
             new String[] { "foob*", "-foo*" },
             Map.of(),
             Map.of(),
@@ -98,7 +94,6 @@ public void testAliasWildcardsIncludeAndExcludeSome() throws Exception {
         final XContentBuilder xContentBuilder = XContentFactory.contentBuilder(XContentType.JSON);
         final AliasMetadata aliasMetadata = AliasMetadata.builder("foo").build();
         final RestResponse restResponse = RestGetAliasesAction.buildRestResponse(
-            true,
             new String[] { "foo*", "-foob*" },
             Map.of("index", List.of(aliasMetadata)),
             Map.of(),
@@ -120,7 +115,6 @@ public void testAliasWildcardsIncludeAndExcludeSomeAndExplicitMissing() throws E
         }
 
         final RestResponse restResponse = RestGetAliasesAction.buildRestResponse(
-            true,
             aliasPattern,
             Map.of("index", List.of(aliasMetadata)),
             Map.of(),
@@ -137,7 +131,6 @@ public void testAliasWildcardsIncludeAndExcludeSomeAndExplicitMissing() throws E
     public void testAliasWildcardsExcludeExplicitMissing() throws Exception {
         final XContentBuilder xContentBuilder = XContentFactory.contentBuilder(XContentType.JSON);
         final RestResponse restResponse = RestGetAliasesAction.buildRestResponse(
-            true,
             new String[] { "foo", "foofoo", "-foo*" },
             Map.of(),
             Map.of(),