Convert MalformedDynamicTemplateIT to unit test (#119647)

Most of MalformedDynamicTemplateIT deals with ignoring unknown
parameters in indices created previous to version 8. While we still need
to check that we can parse those "bad" mappings, we no longer need to
check that we can index into them since v7 indices are read-only.
This change moves the check for leniency and the check for errors
post-v8 to the DynamicTemplatesTests unit test.

Author: cbuescher

server/src/internalClusterTest/java/org/elasticsearch/indices/mapping/MalformedDynamicTemplateIT.java

@@ -21,8 +21,10 @@
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.common.xcontent.XContentHelper;
 import org.elasticsearch.index.IndexVersion;
+import org.elasticsearch.index.IndexVersions;
 import org.elasticsearch.plugins.internal.XContentMeteringParserDecorator;
 import org.elasticsearch.test.XContentTestUtils;
+import org.elasticsearch.test.index.IndexVersionUtils;
 import org.elasticsearch.xcontent.XContentBuilder;
 import org.elasticsearch.xcontent.XContentFactory;
 import org.elasticsearch.xcontent.XContentParser;
@@ -1376,6 +1378,42 @@ public void testSubobjectsFalseWithInnerNestedFromDynamicTemplate() {
         );
     }
 
+    /**
+     * test that bad mapping is accepted for indices created before 8.0.0.
+     * We still need to test this in v9 because of N-2 read compatibility
+     */
+    public void testMalformedDynamicMapping_v7() throws IOException {
+        String mapping = """
+                {
+                    "_doc": {
+                        "dynamic_templates": [
+                            {
+                                "my_template": {
+                                    "mapping": {
+                                        "ignore_malformed": true,
+                                        "type": "keyword"
+                                    },
+                                    "path_match": "*"
+                                }
+                            }
+                        ]
+                    }
+                }
+            """;
+        MapperParsingException ex = expectThrows(MapperParsingException.class, () -> createMapperService(mapping));
+        assertThat(ex.getMessage(), containsString("dynamic template [my_template] has invalid content"));
+
+        // the previous exception should be ignored by indices with v7 index versions
+        IndexVersion indexVersion = IndexVersionUtils.randomPreviousCompatibleVersion(random(), IndexVersions.V_8_0_0);
+        Settings settings = Settings.builder().put("number_of_shards", 1).put("index.version.created", indexVersion).build();
+        MapperService mapperService = createMapperService(indexVersion, settings, () -> randomBoolean());
+        merge(mapperService, mapping);
+        assertWarnings(
+            "Parameter [ignore_malformed] is used in a dynamic template mapping and has no effect on type [keyword]. "
+                + "Usage will result in an error in future major versions and should be removed."
+        );
+    }
+
     public void testSubobjectsAutoFlatPaths() throws IOException {
         assumeTrue("only test when feature flag for subobjects auto is enabled", ObjectMapper.SUB_OBJECTS_AUTO_FEATURE_FLAG.isEnabled());
         MapperService mapperService = createDynamicTemplateAutoSubobjects();