Expose lucene's RemoveDuplicatesTokenFilter (#31275)

docs/reference/analysis/tokenfilters.asciidoc

@@ -95,4 +95,6 @@ include::tokenfilters/decimal-digit-tokenfilter.asciidoc[]
 
 include::tokenfilters/fingerprint-tokenfilter.asciidoc[]
 
-include::tokenfilters/minhash-tokenfilter.asciidoc[]
+include::tokenfilters/minhash-tokenfilter.asciidoc[]
+
+include::tokenfilters/remove-duplicates-tokenfilter.asciidoc[]

docs/reference/analysis/tokenfilters/remove-duplicates-tokenfilter.asciidoc

@@ -0,0 +1,5 @@
+[[analysis-remove-duplicates-tokenfilter]]
+=== Remove Duplicates Token Filter
+
+A token filter of type `remove_duplicates` that drops identical tokens at the
+same position.

modules/analysis-common/src/main/java/org/elasticsearch/analysis/common/CommonAnalysisPlugin.java

@@ -194,6 +194,7 @@ public Map<String, AnalysisProvider<TokenFilterFactory>> getTokenFilters() {
         filters.put("pattern_replace", requriesAnalysisSettings(PatternReplaceTokenFilterFactory::new));
         filters.put("persian_normalization", PersianNormalizationFilterFactory::new);
         filters.put("porter_stem", PorterStemTokenFilterFactory::new);
+        filters.put("remove_duplicates", RemoveDuplicatesTokenFilterFactory::new);
         filters.put("reverse", ReverseTokenFilterFactory::new);
         filters.put("russian_stem", RussianStemTokenFilterFactory::new);
         filters.put("scandinavian_folding", ScandinavianFoldingFilterFactory::new);

modules/analysis-common/src/main/java/org/elasticsearch/analysis/common/RemoveDuplicatesTokenFilterFactory.java

@@ -0,0 +1,42 @@
+/*
+ * Licensed to Elasticsearch under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch licenses this file to you under
+ * the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package org.elasticsearch.analysis.common;
+
+import org.apache.lucene.analysis.TokenStream;
+import org.apache.lucene.analysis.miscellaneous.RemoveDuplicatesTokenFilter;
+import org.elasticsearch.common.settings.Settings;
+import org.elasticsearch.env.Environment;
+import org.elasticsearch.index.IndexSettings;
+import org.elasticsearch.index.analysis.AbstractTokenFilterFactory;
+
+/**
+ * Filter factory for the lucene RemoveDuplicatesTokenFilter
+ */
+class RemoveDuplicatesTokenFilterFactory extends AbstractTokenFilterFactory {
+
+    RemoveDuplicatesTokenFilterFactory(IndexSettings indexSettings, Environment env, String name, Settings settings) {
+        super(indexSettings, name, settings);
+    }
+
+    @Override
+    public TokenStream create(TokenStream tokenStream) {
+        return new RemoveDuplicatesTokenFilter(tokenStream);
+    }
+}

modules/analysis-common/src/test/java/org/elasticsearch/analysis/common/RemoveDuplicatesFilterFactoryTests.java

@@ -0,0 +1,61 @@
+/*
+ * Licensed to Elasticsearch under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch licenses this file to you under
+ * the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package org.elasticsearch.analysis.common;
+
+import org.apache.lucene.analysis.CannedTokenStream;
+import org.apache.lucene.analysis.Token;
+import org.elasticsearch.common.settings.Settings;
+import org.elasticsearch.env.Environment;
+import org.elasticsearch.index.analysis.AnalysisTestsHelper;
+import org.elasticsearch.index.analysis.TokenFilterFactory;
+import org.elasticsearch.test.ESTestCase;
+import org.elasticsearch.test.ESTokenStreamTestCase;
+
+import java.io.IOException;
+
+import static org.hamcrest.Matchers.instanceOf;
+
+public class RemoveDuplicatesFilterFactoryTests extends ESTokenStreamTestCase {
+
+    public void testRemoveDuplicatesFilter() throws IOException {
+        Settings settings = Settings.builder()
+            .put(Environment.PATH_HOME_SETTING.getKey(), createTempDir().toString())
+            .put("index.analysis.filter.removedups.type", "remove_duplicates")
+            .build();
+        ESTestCase.TestAnalysis analysis = AnalysisTestsHelper.createTestAnalysisFromSettings(settings, new CommonAnalysisPlugin());
+        TokenFilterFactory tokenFilter = analysis.tokenFilter.get("removedups");
+        assertThat(tokenFilter, instanceOf(RemoveDuplicatesTokenFilterFactory.class));
+
+        CannedTokenStream cts = new CannedTokenStream(
+            new Token("a", 1, 0, 1),
+            new Token("b", 1, 2, 3),
+            new Token("c", 0, 2, 3),
+            new Token("b", 0, 2, 3),
+            new Token("d", 1, 4, 5)
+        );
+
+        assertTokenStreamContents(tokenFilter.create(cts), new String[]{
+            "a", "b", "c", "d"
+        }, new int[]{
+             1,   1,   0,   1
+        });
+    }
+
+}