Add pre-configured “lowercase” normalizer

docs/reference/analysis/normalizers.asciidoc

@@ -13,11 +13,13 @@ following: `arabic_normalization`, `asciifolding`, `bengali_normalization`,
 `persian_normalization`, `scandinavian_folding`, `serbian_normalization`,
 `sorani_normalization`, `uppercase`.
 
+Elasticsearch ships with a `lowercase` built-in normalizer. For other forms of
+normalization a custom configuration is required.
+
 [float]
 === Custom normalizers
 
-Elasticsearch does not ship with built-in normalizers so far, so the only way
-to get one is by building a custom one. Custom normalizers take a list of char
+Custom normalizers take a list of
 <<analysis-charfilters, character filters>> and a list of
 <<analysis-tokenfilters,token filters>>.
 

docs/reference/mapping/params/normalizer.asciidoc

@@ -7,9 +7,13 @@ produces a single token.
 
 The `normalizer` is applied prior to indexing the keyword, as well as at
 search-time when the `keyword` field is searched via a query parser such as
-the <<query-dsl-match-query,`match`>> query or via a term-level query 
+the <<query-dsl-match-query,`match`>> query or via a term-level query
 such as the <<query-dsl-term-query,`term`>> query.
 
+A simple normalizer called `lowercase` ships with elasticsearch and can be used.
+Custom normalizers can be defined as part of analysis settings as follows.
+
+
 [source,console]
 --------------------------------
 PUT index

server/src/main/java/org/elasticsearch/index/analysis/AnalysisRegistry.java

@@ -293,7 +293,6 @@ private Map<String, AnalyzerProvider<?>> buildAnalyzerFactories(IndexSettings in
 
     private Map<String, AnalyzerProvider<?>> buildNormalizerFactories(IndexSettings indexSettings) throws IOException {
         final Map<String, Settings> normalizersSettings = indexSettings.getSettings().getGroups("index.analysis.normalizer");
-        // TODO: Have pre-built normalizers
         return buildMapping(Component.NORMALIZER, indexSettings, normalizersSettings, normalizers, Collections.emptyMap());
     }
 

server/src/main/java/org/elasticsearch/index/analysis/LowercaseNormalizer.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.index.analysis;
+
+import org.apache.lucene.analysis.Analyzer;
+import org.apache.lucene.analysis.LowerCaseFilter;
+import org.apache.lucene.analysis.TokenStream;
+import org.apache.lucene.analysis.Tokenizer;
+import org.apache.lucene.analysis.core.KeywordTokenizer;
+
+/** Normalizer used to lowercase values */
+public final class LowercaseNormalizer extends Analyzer {
+
+    @Override
+    protected TokenStreamComponents createComponents(String s) {
+        final Tokenizer tokenizer = new KeywordTokenizer();
+        TokenStream stream = new LowerCaseFilter(tokenizer);
+        return new TokenStreamComponents(tokenizer, stream);
+    }
+
+    @Override
+    protected TokenStream normalize(String fieldName, TokenStream in) {
+      return new LowerCaseFilter(in);
+    }          
+}

server/src/main/java/org/elasticsearch/index/analysis/LowercaseNormalizerProvider.java

@@ -0,0 +1,44 @@
+/*
+ * 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.index.analysis;
+
+import org.elasticsearch.common.settings.Settings;
+import org.elasticsearch.env.Environment;
+import org.elasticsearch.index.IndexSettings;
+
+
+/**
+ * Builds an analyzer for normalization that lowercases terms.  
+ */
+public class LowercaseNormalizerProvider extends AbstractIndexAnalyzerProvider<LowercaseNormalizer> {
+
+    private final LowercaseNormalizer analyzer;
+
+    public LowercaseNormalizerProvider(IndexSettings indexSettings, Environment env, String name, Settings settings) {
+        super(indexSettings, name, settings);
+        this.analyzer = new LowercaseNormalizer();
+    }
+
+    @Override
+    public LowercaseNormalizer get() {
+        return analyzer;
+    }
+}

server/src/main/java/org/elasticsearch/indices/analysis/AnalysisModule.java

@@ -35,6 +35,7 @@
 import org.elasticsearch.index.analysis.CharFilterFactory;
 import org.elasticsearch.index.analysis.HunspellTokenFilterFactory;
 import org.elasticsearch.index.analysis.KeywordAnalyzerProvider;
+import org.elasticsearch.index.analysis.LowercaseNormalizerProvider;
 import org.elasticsearch.index.analysis.PreBuiltAnalyzerProviderFactory;
 import org.elasticsearch.index.analysis.PreConfiguredCharFilter;
 import org.elasticsearch.index.analysis.PreConfiguredTokenFilter;
@@ -250,7 +251,7 @@ private NamedRegistry<AnalysisProvider<AnalyzerProvider<?>>> setupAnalyzers(List
 
     private NamedRegistry<AnalysisProvider<AnalyzerProvider<?>>> setupNormalizers(List<AnalysisPlugin> plugins) {
         NamedRegistry<AnalysisProvider<AnalyzerProvider<?>>> normalizers = new NamedRegistry<>("normalizer");
-        // TODO: provide built-in normalizer providers?
+        normalizers.register("lowercase", LowercaseNormalizerProvider::new);
         // TODO: pluggability?
         return normalizers;
     }

server/src/test/java/org/elasticsearch/index/analysis/AnalysisRegistryTests.java

@@ -20,11 +20,13 @@
 package org.elasticsearch.index.analysis;
 
 import com.carrotsearch.randomizedtesting.generators.RandomPicks;
+
 import org.apache.lucene.analysis.Analyzer;
 import org.apache.lucene.analysis.MockTokenFilter;
 import org.apache.lucene.analysis.TokenStream;
 import org.apache.lucene.analysis.Tokenizer;
 import org.apache.lucene.analysis.en.EnglishAnalyzer;
+import org.apache.lucene.analysis.reverse.ReverseStringFilter;
 import org.apache.lucene.analysis.standard.StandardAnalyzer;
 import org.apache.lucene.analysis.standard.StandardTokenizer;
 import org.apache.lucene.analysis.tokenattributes.CharTermAttribute;
@@ -39,12 +41,14 @@
 import org.elasticsearch.indices.analysis.AnalysisModule.AnalysisProvider;
 import org.elasticsearch.indices.analysis.PreBuiltAnalyzers;
 import org.elasticsearch.plugins.AnalysisPlugin;
+import org.elasticsearch.plugins.Plugin;
 import org.elasticsearch.test.ESTestCase;
 import org.elasticsearch.test.IndexSettingsModule;
 import org.elasticsearch.test.VersionUtils;
 
 import java.io.IOException;
 import java.util.Collections;
+import java.util.List;
 import java.util.Map;
 
 import static java.util.Collections.emptyMap;
@@ -57,6 +61,7 @@
 
 public class AnalysisRegistryTests extends ESTestCase {
     private AnalysisRegistry emptyRegistry;
+    private AnalysisRegistry nonEmptyRegistry;
 
     private static AnalyzerProvider<?> analyzerProvider(final String name) {
         return new PreBuiltAnalyzerProvider(name, AnalyzerScope.INDEX, new EnglishAnalyzer());
@@ -67,6 +72,16 @@ private static AnalysisRegistry emptyAnalysisRegistry(Settings settings) {
                 emptyMap(), emptyMap(), emptyMap(), emptyMap());
     }
 
+    /**
+     * Creates a reverse filter available for use in testNameClashNormalizer test
+     */
+    public static class MockAnalysisPlugin extends Plugin implements AnalysisPlugin {
+        @Override
+        public List<PreConfiguredTokenFilter> getPreConfiguredTokenFilters() {
+            return singletonList(PreConfiguredTokenFilter.singleton("reverse", true, ReverseStringFilter::new));
+        }
+    }    
+
     private static IndexSettings indexSettingsOfCurrentVersion(Settings.Builder settings) {
         return IndexSettingsModule.newIndexSettings("index", settings
                 .put(IndexMetadata.SETTING_VERSION_CREATED, Version.CURRENT)
@@ -76,9 +91,13 @@ private static IndexSettings indexSettingsOfCurrentVersion(Settings.Builder sett
     @Override
     public void setUp() throws Exception {
         super.setUp();
-        emptyRegistry = emptyAnalysisRegistry(Settings.builder()
+        Settings settings = Settings.builder()
                 .put(Environment.PATH_HOME_SETTING.getKey(), createTempDir().toString())
-                .build());
+                .build();
+        emptyRegistry = emptyAnalysisRegistry(settings);
+        // Module loaded to register in-built normalizers for testing
+        AnalysisModule module = new AnalysisModule(TestEnvironment.newEnvironment(settings), singletonList(new MockAnalysisPlugin()));
+        nonEmptyRegistry = module.getAnalysisRegistry();
     }
 
     public void testDefaultAnalyzers() throws IOException {
@@ -134,7 +153,29 @@ public Tokenizer create() {
                         emptyMap(), emptyMap(), emptyMap()));
         assertEquals("analyzer [default] contains filters [my_filter] that are not allowed to run in all mode.", ex.getMessage());
     }
+
+
+    public void testNameClashNormalizer() throws IOException {
+
+        // Test out-of-the-box normalizer works OK.
+        IndexAnalyzers indexAnalyzers = nonEmptyRegistry.build(IndexSettingsModule.newIndexSettings("index", Settings.EMPTY));
+        assertNotNull(indexAnalyzers.getNormalizer("lowercase"));
+        assertThat(indexAnalyzers.getNormalizer("lowercase").normalize("field", "AbC").utf8ToString(), equalTo("abc"));
+
+        // Test that a name clash with a custom normalizer will favour the index's normalizer rather than the out-of-the-box 
+        // one of the same name. (However this "feature" will be removed with https://github.com/elastic/elasticsearch/issues/22263 ) 
+        Settings settings = Settings.builder()
+            // Deliberately bad choice of normalizer name for the job it does.
+            .put("index.analysis.normalizer.lowercase.type", "custom")
+            .putList("index.analysis.normalizer.lowercase.filter", "reverse")
+            .build();
+
+        indexAnalyzers = nonEmptyRegistry.build(IndexSettingsModule.newIndexSettings("index", settings));
+        assertNotNull(indexAnalyzers.getNormalizer("lowercase"));
+        assertThat(indexAnalyzers.getNormalizer("lowercase").normalize("field","AbC").utf8ToString(), equalTo("CbA"));
+    }       
 
+
     public void testOverrideDefaultIndexAnalyzerIsUnsupported() {
         Version version = VersionUtils.randomIndexCompatibleVersion(random());
         Settings settings = Settings.builder().put(IndexMetadata.SETTING_VERSION_CREATED, version).build();

server/src/test/java/org/elasticsearch/index/mapper/KeywordFieldMapperTests.java

@@ -344,10 +344,18 @@ public void testEnableNorms() throws IOException {
         assertEquals(0, fieldNamesFields.length);
     }
 
-    public void testNormalizer() throws IOException {
+    public void testCustomNormalizer() throws IOException {
+        checkLowercaseNormalizer("my_lowercase");
+    }
+
+    public void testInBuiltNormalizer() throws IOException {
+        checkLowercaseNormalizer("lowercase");        
+    }       
+
+    public void checkLowercaseNormalizer(String normalizerName) throws IOException {
         String mapping = Strings.toString(XContentFactory.jsonBuilder().startObject().startObject("type")
                 .startObject("properties").startObject("field")
-                .field("type", "keyword").field("normalizer", "my_lowercase").endObject().endObject()
+                .field("type", "keyword").field("normalizer", normalizerName).endObject().endObject()
                 .endObject().endObject());
 
         DocumentMapper mapper = parser.parse("type", new CompressedXContent(mapping));