[9.0] refactor(semantic_text): fail early in pre-8.11 indices (#133080)

docs/changelog/133080.yaml

@@ -0,0 +1,5 @@
+pr: 133080
+summary: "Disallow creating `semantic_text` fields in indices created prior to 8.11.0"
+area: Relevance
+type: bug
+issues: []

x-pack/plugin/inference/src/main/java/org/elasticsearch/xpack/inference/mapper/SemanticTextFieldMapper.java

@@ -7,6 +7,8 @@
 
 package org.elasticsearch.xpack.inference.mapper;
 
+import org.apache.logging.log4j.LogManager;
+import org.apache.logging.log4j.Logger;
 import org.apache.lucene.index.FieldInfos;
 import org.apache.lucene.index.LeafReaderContext;
 import org.apache.lucene.search.DocIdSetIterator;
@@ -89,6 +91,7 @@
 import java.util.function.BiConsumer;
 import java.util.function.Function;
 
+import static org.elasticsearch.index.IndexVersions.NEW_SPARSE_VECTOR;
 import static org.elasticsearch.inference.TaskType.SPARSE_EMBEDDING;
 import static org.elasticsearch.inference.TaskType.TEXT_EMBEDDING;
 import static org.elasticsearch.search.SearchService.DEFAULT_SIZE;
@@ -110,6 +113,8 @@
  * A {@link FieldMapper} for semantic text fields.
  */
 public class SemanticTextFieldMapper extends FieldMapper implements InferenceFieldMapper {
+    private static final Logger logger = LogManager.getLogger(SemanticTextFieldMapper.class);
+    public static final String UNSUPPORTED_INDEX_MESSAGE = "[semantic_text] is available on indices created with 8.11 or higher.";
     public static final NodeFeature SEMANTIC_TEXT_IN_OBJECT_FIELD_FIX = new NodeFeature("semantic_text.in_object_field_fix");
     public static final NodeFeature SEMANTIC_TEXT_SINGLE_FIELD_UPDATE_FIX = new NodeFeature("semantic_text.single_field_update_fix");
     public static final NodeFeature SEMANTIC_TEXT_DELETE_FIX = new NodeFeature("semantic_text.delete_fix");
@@ -129,6 +134,9 @@ public class SemanticTextFieldMapper extends FieldMapper implements InferenceFie
 
     public static BiConsumer<String, MappingParserContext> validateParserContext(String type) {
         return (n, c) -> {
+            if (c.getIndexSettings().getIndexVersionCreated().before(NEW_SPARSE_VECTOR)) {
+                throw new UnsupportedOperationException(UNSUPPORTED_INDEX_MESSAGE);
+            }
             if (InferenceMetadataFieldsMapper.isEnabled(c.getIndexSettings().getSettings()) == false) {
                 notInMultiFields(type).accept(n, c);
             }

x-pack/plugin/inference/src/test/java/org/elasticsearch/xpack/inference/mapper/SemanticTextFieldMapperTests.java

@@ -92,6 +92,7 @@
 import static org.elasticsearch.xpack.inference.mapper.SemanticTextField.getChunksFieldName;
 import static org.elasticsearch.xpack.inference.mapper.SemanticTextField.getEmbeddingsFieldName;
 import static org.elasticsearch.xpack.inference.mapper.SemanticTextFieldMapper.DEFAULT_ELSER_2_INFERENCE_ID;
+import static org.elasticsearch.xpack.inference.mapper.SemanticTextFieldMapper.UNSUPPORTED_INDEX_MESSAGE;
 import static org.elasticsearch.xpack.inference.mapper.SemanticTextFieldTests.randomSemanticText;
 import static org.hamcrest.Matchers.containsString;
 import static org.hamcrest.Matchers.equalTo;
@@ -339,6 +340,57 @@ public void testInvalidTaskTypes() {
         }
     }
 
+    @Override
+    protected IndexVersion boostNotAllowedIndexVersion() {
+        return IndexVersions.NEW_SPARSE_VECTOR;
+    }
+
+    public void testOldIndexSemanticTextDenseVectorRaisesError() throws IOException {
+        final String fieldName = "field";
+        final XContentBuilder fieldMapping = fieldMapping(b -> {
+            b.field("type", "semantic_text");
+            b.field(INFERENCE_ID_FIELD, "test_inference_id");
+            b.startObject("model_settings");
+            b.field("task_type", "text_embedding");
+            b.field("dimensions", 384);
+            b.field("similarity", "cosine");
+            b.field("element_type", "float");
+            b.endObject();
+        });
+        assertOldIndexUnsupported(fieldMapping);
+    }
+
+    public void testOldIndexSemanticTextMinimalMappingRaisesError() throws IOException {
+        final XContentBuilder fieldMapping = fieldMapping(this::minimalMapping);
+        assertOldIndexUnsupported(fieldMapping);
+    }
+
+    public void testOldIndexSemanticTextSparseVersionRaisesError() throws IOException {
+        final XContentBuilder fieldMapping = fieldMapping(b -> {
+            b.field("type", "semantic_text");
+            b.field("inference_id", "another_inference_id");
+            b.startObject("model_settings");
+            b.field("task_type", "sparse_embedding");
+            b.endObject();
+        });
+        assertOldIndexUnsupported(fieldMapping);
+    }
+
+    private void assertOldIndexUnsupported(XContentBuilder fieldMapping) {
+
+        MapperParsingException exception = assertThrows(
+            MapperParsingException.class,
+            () -> createMapperService(
+                fieldMapping,
+                true,
+                IndexVersions.V_8_0_0,
+                IndexVersionUtils.getPreviousVersion(IndexVersions.NEW_SPARSE_VECTOR)
+            )
+        );
+        assertTrue(exception.getMessage().contains(UNSUPPORTED_INDEX_MESSAGE));
+        assertTrue(exception.getRootCause() instanceof UnsupportedOperationException);
+    }
+
     public void testMultiFieldsSupport() throws IOException {
         if (useLegacyFormat) {
             Exception e = expectThrows(MapperParsingException.class, () -> createMapperService(fieldMapping(b -> {