Add back version based logic from IndexSortConfig

This change re-introduces pre-7.13 deprecation logging and silent handling
of index sorting on alias fields. We need to still support this for v9 for read-only
indices.

Author: cbuescher

server/src/main/java/org/elasticsearch/index/IndexSortConfig.java

@@ -14,6 +14,8 @@
 import org.apache.lucene.search.SortedNumericSortField;
 import org.apache.lucene.search.SortedSetSortField;
 import org.elasticsearch.cluster.metadata.DataStream;
+import org.elasticsearch.common.logging.DeprecationCategory;
+import org.elasticsearch.common.logging.DeprecationLogger;
 import org.elasticsearch.common.settings.Setting;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.index.fielddata.IndexFieldData;
@@ -53,6 +55,8 @@
 **/
 public final class IndexSortConfig {
 
+    private static final DeprecationLogger DEPRECATION_LOGGER = DeprecationLogger.getLogger(IndexSortConfig.class);
+
     /**
      * The list of field names
      */
@@ -134,10 +138,14 @@ private static MultiValueMode parseMultiValueMode(String value) {
 
     // visible for tests
     final FieldSortSpec[] sortSpecs;
+    private final IndexVersion indexCreatedVersion;
+    private final String indexName;
     private final IndexMode indexMode;
 
     public IndexSortConfig(IndexSettings indexSettings) {
         final Settings settings = indexSettings.getSettings();
+        this.indexCreatedVersion = indexSettings.getIndexVersionCreated();
+        this.indexName = indexSettings.getIndex().getName();
         this.indexMode = indexSettings.getMode();
 
         if (this.indexMode == IndexMode.TIME_SERIES) {
@@ -230,7 +238,22 @@ public Sort buildIndexSort(
                 throw new IllegalArgumentException(err);
             }
             if (Objects.equals(ft.name(), sortSpec.field) == false) {
-                throw new IllegalArgumentException("Cannot use alias [" + sortSpec.field + "] as an index sort field");
+                if (this.indexCreatedVersion.onOrAfter(IndexVersions.V_7_13_0)) {
+                    throw new IllegalArgumentException("Cannot use alias [" + sortSpec.field + "] as an index sort field");
+                } else {
+                    DEPRECATION_LOGGER.warn(
+                        DeprecationCategory.MAPPINGS,
+                        "index-sort-aliases",
+                        "Index sort for index ["
+                            + indexName
+                            + "] defined on field ["
+                            + sortSpec.field
+                            + "] which resolves to field ["
+                            + ft.name()
+                            + "]. "
+                            + "You will not be able to define an index sort over aliased fields in new indexes"
+                    );
+                }
             }
             boolean reverse = sortSpec.order == null ? false : (sortSpec.order == SortOrder.DESC);
             MultiValueMode mode = sortSpec.mode;

server/src/test/java/org/elasticsearch/index/IndexSortSettingsTests.java

@@ -160,6 +160,20 @@ public void testSortingAgainstAliases() {
         assertEquals("Cannot use alias [field] as an index sort field", e.getMessage());
     }
 
+    public void testSortingAgainstAliasesPre713() {
+        IndexSettings indexSettings = indexSettings(
+            Settings.builder().put(IndexMetadata.SETTING_VERSION_CREATED, IndexVersions.V_7_12_0).put("index.sort.field", "field").build()
+        );
+        MappedFieldType aliased = new KeywordFieldMapper.KeywordFieldType("aliased");
+        Sort sort = buildIndexSort(indexSettings, Map.of("field", aliased));
+        assertThat(sort.getSort(), arrayWithSize(1));
+        assertThat(sort.getSort()[0].getField(), equalTo("aliased"));
+        assertWarnings(
+            "Index sort for index [test] defined on field [field] which resolves to field [aliased]. "
+                + "You will not be able to define an index sort over aliased fields in new indexes"
+        );
+    }
+
     public void testTimeSeriesMode() {
         IndexSettings indexSettings = indexSettings(
             Settings.builder()