Remove TODO in IndexNameExpressionResolver (#52963)

This commit removes a TODO in the IndexNameExpressionResolver that
indicated the API should use a Set instead of a List. However, this
TODO was not completely correct since the ordering of arguments matters
due to negations when evaluating wildcards and since we also allow
a list of patterns like `*,-foo,*`, which would have a different
meaning even when using a Set with insertion ordering.

Relates #52788

server/src/main/java/org/elasticsearch/cluster/metadata/IndexNameExpressionResolver.java

@@ -680,8 +680,6 @@ public class IndexNameExpressionResolver {
                 return resolveEmptyOrTrivialWildcard(options, metaData);
             }
 
-            // TODO: Fix API to work with sets rather than lists since we need to convert to sets
-            // internally anyway.
             Set<String> result = innerResolve(context, expressions, options, metaData);
 
             if (result == null) {

server/src/test/java/org/elasticsearch/cluster/metadata/IndexNameExpressionResolverTests.java

@@ -351,6 +351,10 @@ public class IndexNameExpressionResolverTests extends ESTestCase {
         assertEquals(1, results.length);
         assertEquals("bar", results[0]);
 
+        results = indexNameExpressionResolver.concreteIndexNames(context, "*", "-foo", "*");
+        assertEquals(3, results.length);
+        assertThat(results, arrayContainingInAnyOrder("bar", "foobar", "foo"));
+
         results = indexNameExpressionResolver.concreteIndexNames(context, "-*");
         assertEquals(0, results.length);