Deprecate _type from LeafDocLookup (#37491)

* Deprecate _type from LeafDocLookup

* Response to PR comments.

* Response to PR comments.

Author: jdconrad

server/src/main/java/org/elasticsearch/search/lookup/LeafDocLookup.java

@@ -18,9 +18,11 @@
  */
 package org.elasticsearch.search.lookup;
 
+import org.apache.logging.log4j.LogManager;
 import org.apache.lucene.index.LeafReaderContext;
 import org.elasticsearch.ExceptionsHelper;
 import org.elasticsearch.common.Nullable;
+import org.elasticsearch.common.logging.DeprecationLogger;
 import org.elasticsearch.index.fielddata.IndexFieldData;
 import org.elasticsearch.index.fielddata.ScriptDocValues;
 import org.elasticsearch.index.mapper.MappedFieldType;
@@ -38,6 +40,12 @@
 
 public class LeafDocLookup implements Map<String, ScriptDocValues<?>> {
 
+    private static final DeprecationLogger DEPRECATION_LOGGER
+            = new DeprecationLogger(LogManager.getLogger(LeafDocLookup.class));
+    static final String TYPES_DEPRECATION_KEY = "type-field-doc-lookup";
+    static final String TYPES_DEPRECATION_MESSAGE =
+            "[types removal] Looking up doc types in scripts is deprecated.";
+
     private final Map<String, ScriptDocValues<?>> localCacheFieldData = new HashMap<>(4);
 
     private final MapperService mapperService;
@@ -72,6 +80,10 @@ public void setDocument(int docId) {
 
     @Override
     public ScriptDocValues<?> get(Object key) {
+        // deprecate _type
+        if ("_type".equals(key)) {
+            DEPRECATION_LOGGER.deprecatedAndMaybeLog(TYPES_DEPRECATION_KEY, TYPES_DEPRECATION_MESSAGE);
+        }
         // assume its a string...
         String fieldName = key.toString();
         ScriptDocValues<?> scriptValues = localCacheFieldData.get(fieldName);

server/src/test/java/org/elasticsearch/search/lookup/LeafDocLookupTests.java

@@ -26,6 +26,7 @@
 import org.elasticsearch.test.ESTestCase;
 import org.junit.Before;
 
+import static org.elasticsearch.search.lookup.LeafDocLookup.TYPES_DEPRECATION_MESSAGE;
 import static org.mockito.AdditionalAnswers.returnsFirstArg;
 import static org.mockito.Matchers.anyObject;
 import static org.mockito.Mockito.doReturn;
@@ -45,6 +46,7 @@ public void setUp() throws Exception {
         when(fieldType.valueForDisplay(anyObject())).then(returnsFirstArg());
 
         MapperService mapperService = mock(MapperService.class);
+        when(mapperService.fullName("_type")).thenReturn(fieldType);
         when(mapperService.fullName("field")).thenReturn(fieldType);
         when(mapperService.fullName("alias")).thenReturn(fieldType);
 
@@ -72,4 +74,10 @@ public void testLookupWithFieldAlias() {
         ScriptDocValues<?> fetchedDocValues = docLookup.get("alias");
         assertEquals(docValues, fetchedDocValues);
     }
+
+    public void testTypesDeprecation() {
+        ScriptDocValues<?> fetchedDocValues = docLookup.get("_type");
+        assertEquals(docValues, fetchedDocValues);
+        assertWarnings(TYPES_DEPRECATION_MESSAGE);
+    }
 }