Improve error message for parse failures of completion fields (#27297)

Fix spacing/grammar/punctuation, and include the field name and location in the source document.

core/src/main/java/org/elasticsearch/index/mapper/CompletionFieldMapper.java

@@ -30,9 +30,9 @@ import org.apache.lucene.search.suggest.document.FuzzyCompletionQuery;
 import org.apache.lucene.search.suggest.document.PrefixCompletionQuery;
 import org.apache.lucene.search.suggest.document.RegexCompletionQuery;
 import org.apache.lucene.search.suggest.document.SuggestField;
-import org.elasticsearch.ElasticsearchParseException;
 import org.elasticsearch.Version;
 import org.elasticsearch.common.ParseField;
+import org.elasticsearch.common.ParsingException;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.common.unit.Fuzziness;
 import org.elasticsearch.common.util.set.Sets;
@@ -560,7 +560,7 @@ public class CompletionFieldMapper extends FieldMapper implements ArrayValueMapp
                 }
             }
         } else {
-            throw new ElasticsearchParseException("failed to parse expected text or object got" + token.name());
+            throw new ParsingException(parser.getTokenLocation(), "failed to parse [" + parser.currentName() + "]: expected text or object, but got " + token.name());
         }
     }
 

core/src/test/java/org/elasticsearch/index/mapper/CompletionFieldMapperTests.java

@@ -163,6 +163,25 @@ public class CompletionFieldMapperTests extends ESSingleNodeTestCase {
         assertSuggestFields(fields, 1);
     }
 
+    public void testParsingFailure() throws Exception {
+        String mapping = jsonBuilder().startObject().startObject("type1")
+            .startObject("properties").startObject("completion")
+            .field("type", "completion")
+            .endObject().endObject()
+            .endObject().endObject().string();
+
+        DocumentMapper defaultMapper = createIndex("test").mapperService().documentMapperParser().parse("type1", new CompressedXContent(mapping));
+
+        MapperParsingException e = expectThrows(MapperParsingException.class, () ->
+            defaultMapper.parse(SourceToParse.source("test", "type1", "1", XContentFactory.jsonBuilder()
+                    .startObject()
+                    .field("completion", 1.0)
+                    .endObject()
+                    .bytes(),
+                XContentType.JSON)));
+        assertEquals("failed to parse [completion]: expected text or object, but got VALUE_NUMBER", e.getCause().getMessage());
+    }
+
     public void testParsingMultiValued() throws Exception {
         String mapping = jsonBuilder().startObject().startObject("type1")
                 .startObject("properties").startObject("completion")