Added lenient flag for synonym token filter

docs/reference/analysis/tokenfilters/synonym-graph-tokenfilter.asciidoc

@@ -50,7 +50,49 @@ PUT /test_index
 The above configures a `search_synonyms` filter, with a path of
 `analysis/synonym.txt` (relative to the `config` location). The
 `search_synonyms` analyzer is then configured with the filter.
-Additional settings are: `expand` (defaults to `true`).
+
+Additional settings are:
+
+* `expand` (defaults to `true`).
+* `lenient` (defaults to `false`). If `true` ignores exceptions while parsing the synonym configuration. It is important
+to note that only those synonym rules which cannot get parsed are ignored. For instance consider the following request:
+
+[source,js]
+--------------------------------------------------
+PUT /test_index
+{
+    "settings": {
+        "index" : {
+            "analysis" : {
+                "analyzer" : {
+                    "synonym" : {
+                        "tokenizer" : "standard",
+                        "filter" : ["my_stop", "synonym_graph"]
+                    }
+                },
+                "filter" : {
+                	"my_stop": {
+                		"type" : "stop",
+                		"stopwords": ["bar"]
+                	},
+                    "synonym_graph" : {
+                        "type" : "synonym_graph",
+                        "lenient": true,
+                        "synonyms" : ["foo, bar => baz"]
+                    }
+                }
+            }
+        }
+    }
+}
+--------------------------------------------------
+// CONSOLE
+With the above request the word `bar` gets skipped but a mapping `foo => baz` is still added. However, if the mapping
+being added was "foo, baz => bar" nothing would get added to the synonym list. This is because the target word for the
+mapping is itself eliminated because it was a stop word. Similarly, if the mapping was "bar, foo, baz" and `expand` was
+set to `false` no mapping would get added as when `expand=false` the target mapping is the first word. However, if
+`expand=true` then the mappings added would be equivalent to `foo, baz => foo, baz` i.e, all mappings other than the
+stop word.
 
 [float]
 ==== `tokenizer` and `ignore_case` are deprecated

docs/reference/analysis/tokenfilters/synonym-tokenfilter.asciidoc

@@ -33,12 +33,55 @@ PUT /test_index
 
 The above configures a `synonym` filter, with a path of
 `analysis/synonym.txt` (relative to the `config` location). The
-`synonym` analyzer is then configured with the filter. Additional
-settings is: `expand` (defaults to `true`).
+`synonym` analyzer is then configured with the filter.
 
 This filter tokenize synonyms with whatever tokenizer and token filters
 appear before it in the chain.
 
+Additional settings are:
+
+* `expand` (defaults to `true`).
+* `lenient` (defaults to `false`). If `true` ignores exceptions while parsing the synonym configuration. It is important
+to note that only those synonym rules which cannot get parsed are ignored. For instance consider the following request:
+
+[source,js]
+--------------------------------------------------
+PUT /test_index
+{
+    "settings": {
+        "index" : {
+            "analysis" : {
+                "analyzer" : {
+                    "synonym" : {
+                        "tokenizer" : "standard",
+                        "filter" : ["my_stop", "synonym"]
+                    }
+                },
+                "filter" : {
+                	"my_stop": {
+                		"type" : "stop",
+                		"stopwords": ["bar"]
+                	},
+                    "synonym" : {
+                        "type" : "synonym",
+                        "lenient": true,
+                        "synonyms" : ["foo, bar => baz"]
+                    }
+                }
+            }
+        }
+    }
+}
+--------------------------------------------------
+// CONSOLE
+With the above request the word `bar` gets skipped but a mapping `foo => baz` is still added. However, if the mapping
+being added was "foo, baz => bar" nothing would get added to the synonym list. This is because the target word for the
+mapping is itself eliminated because it was a stop word. Similarly, if the mapping was "bar, foo, baz" and `expand` was
+set to `false` no mapping would get added as when `expand=false` the target mapping is the first word. However, if
+`expand=true` then the mappings added would be equivalent to `foo, baz => foo, baz` i.e, all mappings other than the
+stop word.
+
+
 [float]
 ==== `tokenizer` and `ignore_case` are deprecated
 

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

@@ -0,0 +1,68 @@
+/*
+ * 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.logging.log4j.Logger;
+import org.apache.lucene.analysis.Analyzer;
+import org.apache.lucene.analysis.synonym.SolrSynonymParser;
+import org.apache.lucene.util.CharsRef;
+import org.apache.lucene.util.CharsRefBuilder;
+import org.elasticsearch.common.logging.Loggers;
+
+import java.io.IOException;
+
+public class ESSolrSynonymParser extends SolrSynonymParser {
+
+    private final boolean lenient;
+    private static final Logger logger =
+        Loggers.getLogger(ESSolrSynonymParser.class, "ESSolrSynonymParser");
+
+    public ESSolrSynonymParser(boolean dedup, boolean expand, boolean lenient, Analyzer analyzer) {
+        super(dedup, expand, analyzer);
+        this.lenient = lenient;
+    }
+
+    @Override
+    public void add(CharsRef input, CharsRef output, boolean includeOrig) {
+        // This condition follows up on the overridden analyze method. In case lenient was set to true and there was an
+        // exception during super.analyze we return a zero-length CharsRef for that word which caused an exception. When
+        // the synonym mappings for the words are added using the add method we skip the ones that were left empty by
+        // analyze i.e., in the case when lenient is set we only add those combinations which are non-zero-length. The
+        // else would happen only in the case when the input or output is empty and lenient is set, in which case we
+        // quietly ignore it. For more details on the control-flow see SolrSynonymParser::addInternal.
+        if (lenient == false || (input.length > 0 && output.length > 0)) {
+            super.add(input, output, includeOrig);
+        }
+    }
+
+    @Override
+    public CharsRef analyze(String text, CharsRefBuilder reuse) throws IOException {
+        try {
+            return super.analyze(text, reuse);
+        } catch (IllegalArgumentException ex) {
+            if (lenient) {
+                logger.info("Synonym rule for [" + text + "] was ignored");
+                return new CharsRef("");
+            } else {
+                throw ex;
+            }
+        }
+    }
+}

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

@@ -0,0 +1,68 @@
+/*
+ * 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.logging.log4j.Logger;
+import org.apache.lucene.analysis.Analyzer;
+import org.apache.lucene.analysis.synonym.WordnetSynonymParser;
+import org.apache.lucene.util.CharsRef;
+import org.apache.lucene.util.CharsRefBuilder;
+import org.elasticsearch.common.logging.Loggers;
+
+import java.io.IOException;
+
+public class ESWordnetSynonymParser extends WordnetSynonymParser {
+
+    private final boolean lenient;
+    private static final Logger logger =
+        Loggers.getLogger(ESSolrSynonymParser.class, "ESWordnetSynonymParser");
+
+    public ESWordnetSynonymParser(boolean dedup, boolean expand, boolean lenient, Analyzer analyzer) {
+        super(dedup, expand, analyzer);
+        this.lenient = lenient;
+    }
+
+    @Override
+    public void add(CharsRef input, CharsRef output, boolean includeOrig) {
+        // This condition follows up on the overridden analyze method. In case lenient was set to true and there was an
+        // exception during super.analyze we return a zero-length CharsRef for that word which caused an exception. When
+        // the synonym mappings for the words are added using the add method we skip the ones that were left empty by
+        // analyze i.e., in the case when lenient is set we only add those combinations which are non-zero-length. The
+        // else would happen only in the case when the input or output is empty and lenient is set, in which case we
+        // quietly ignore it. For more details on the control-flow see SolrSynonymParser::addInternal.
+        if (lenient == false || (input.length > 0 && output.length > 0)) {
+            super.add(input, output, includeOrig);
+        }
+    }
+
+    @Override
+    public CharsRef analyze(String text, CharsRefBuilder reuse) throws IOException {
+        try {
+            return super.analyze(text, reuse);
+        } catch (IllegalArgumentException ex) {
+            if (lenient) {
+                logger.info("Synonym rule for [" + text + "] was ignored");
+                return new CharsRef("");
+            } else {
+                throw ex;
+            }
+        }
+    }
+}

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

@@ -21,10 +21,8 @@
 
 import org.apache.lucene.analysis.Analyzer;
 import org.apache.lucene.analysis.TokenStream;
-import org.apache.lucene.analysis.synonym.SolrSynonymParser;
 import org.apache.lucene.analysis.synonym.SynonymGraphFilter;
 import org.apache.lucene.analysis.synonym.SynonymMap;
-import org.apache.lucene.analysis.synonym.WordnetSynonymParser;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.env.Environment;
 import org.elasticsearch.index.IndexSettings;
@@ -58,11 +56,11 @@ public Factory(String name, final Analyzer analyzerForParseSynonym, Reader rules
             try {
                 SynonymMap.Builder parser;
                 if ("wordnet".equalsIgnoreCase(format)) {
-                    parser = new WordnetSynonymParser(true, expand, analyzerForParseSynonym);
-                    ((WordnetSynonymParser) parser).parse(rulesReader);
+                    parser = new ESWordnetSynonymParser(true, expand, lenient, analyzerForParseSynonym);
+                    ((ESWordnetSynonymParser) parser).parse(rulesReader);
                 } else {
-                    parser = new SolrSynonymParser(true, expand, analyzerForParseSynonym);
-                    ((SolrSynonymParser) parser).parse(rulesReader);
+                    parser = new ESSolrSynonymParser(true, expand, lenient, analyzerForParseSynonym);
+                    ((ESSolrSynonymParser) parser).parse(rulesReader);
                 }
                 synonymMap = parser.build();
             } catch (Exception e) {

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

@@ -21,10 +21,8 @@
 
 import org.apache.lucene.analysis.Analyzer;
 import org.apache.lucene.analysis.TokenStream;
-import org.apache.lucene.analysis.synonym.SolrSynonymParser;
 import org.apache.lucene.analysis.synonym.SynonymFilter;
 import org.apache.lucene.analysis.synonym.SynonymMap;
-import org.apache.lucene.analysis.synonym.WordnetSynonymParser;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.env.Environment;
 import org.elasticsearch.index.IndexSettings;
@@ -38,6 +36,7 @@ public class SynonymTokenFilterFactory extends AbstractTokenFilterFactory {
 
     protected final String format;
     protected final boolean expand;
+    protected final boolean lenient;
     protected final Settings settings;
 
     public SynonymTokenFilterFactory(IndexSettings indexSettings, Environment env, AnalysisRegistry analysisRegistry,
@@ -52,6 +51,7 @@ public SynonymTokenFilterFactory(IndexSettings indexSettings, Environment env, A
         }
 
         this.expand = settings.getAsBoolean("expand", true);
+        this.lenient = settings.getAsBoolean("lenient", false);
         this.format = settings.get("format", "");
     }
 
@@ -93,11 +93,11 @@ public Factory(String name, Analyzer analyzerForParseSynonym, Reader rulesReader
             try {
                 SynonymMap.Builder parser;
                 if ("wordnet".equalsIgnoreCase(format)) {
-                    parser = new WordnetSynonymParser(true, expand, analyzerForParseSynonym);
-                    ((WordnetSynonymParser) parser).parse(rulesReader);
+                    parser = new ESWordnetSynonymParser(true, expand, lenient, analyzerForParseSynonym);
+                    ((ESWordnetSynonymParser) parser).parse(rulesReader);
                 } else {
-                    parser = new SolrSynonymParser(true, expand, analyzerForParseSynonym);
-                    ((SolrSynonymParser) parser).parse(rulesReader);
+                    parser = new ESSolrSynonymParser(true, expand, lenient, analyzerForParseSynonym);
+                    ((ESSolrSynonymParser) parser).parse(rulesReader);
                 }
                 synonymMap = parser.build();
             } catch (Exception e) {

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

@@ -0,0 +1,78 @@
+/*
+ * 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.CharArraySet;
+import org.apache.lucene.analysis.StopFilter;
+import org.apache.lucene.analysis.TokenStream;
+import org.apache.lucene.analysis.Tokenizer;
+import org.apache.lucene.analysis.standard.StandardAnalyzer;
+import org.apache.lucene.analysis.standard.StandardTokenizer;
+import org.apache.lucene.analysis.synonym.SynonymFilter;
+import org.apache.lucene.analysis.synonym.SynonymMap;
+import org.elasticsearch.test.ESTokenStreamTestCase;
+
+import java.io.IOException;
+import java.io.StringReader;
+import java.text.ParseException;
+
+import static org.hamcrest.Matchers.containsString;
+
+public class ESSolrSynonymParserTests extends ESTokenStreamTestCase {
+
+    public void testLenientParser() throws IOException, ParseException {
+        ESSolrSynonymParser parser = new ESSolrSynonymParser(true, false, true, new StandardAnalyzer());
+        String rules =
+            "&,and\n" +
+            "come,advance,approach\n";
+        StringReader rulesReader = new StringReader(rules);
+        parser.parse(rulesReader);
+        SynonymMap synonymMap = parser.build();
+        Tokenizer tokenizer = new StandardTokenizer();
+        tokenizer.setReader(new StringReader("approach quietly then advance & destroy"));
+        TokenStream ts = new SynonymFilter(tokenizer, synonymMap, false);
+        assertTokenStreamContents(ts, new String[]{"come", "quietly", "then", "come", "destroy"});
+    }
+
+    public void testLenientParserWithSomeIncorrectLines() throws IOException, ParseException {
+        CharArraySet stopSet = new CharArraySet(1, true);
+        stopSet.add("bar");
+        ESSolrSynonymParser parser =
+            new ESSolrSynonymParser(true, false, true, new StandardAnalyzer(stopSet));
+        String rules = "foo,bar,baz";
+        StringReader rulesReader = new StringReader(rules);
+        parser.parse(rulesReader);
+        SynonymMap synonymMap = parser.build();
+        Tokenizer tokenizer = new StandardTokenizer();
+        tokenizer.setReader(new StringReader("first word is foo, then bar and lastly baz"));
+        TokenStream ts = new SynonymFilter(new StopFilter(tokenizer, stopSet), synonymMap, false);
+        assertTokenStreamContents(ts, new String[]{"first", "word", "is", "foo", "then", "and", "lastly", "foo"});
+    }
+
+    public void testNonLenientParser() {
+        ESSolrSynonymParser parser = new ESSolrSynonymParser(true, false, false, new StandardAnalyzer());
+        String rules =
+            "&,and=>and\n" +
+            "come,advance,approach\n";
+        StringReader rulesReader = new StringReader(rules);
+        ParseException ex = expectThrows(ParseException.class, () -> parser.parse(rulesReader));
+        assertThat(ex.getMessage(), containsString("Invalid synonym rule at line 1"));
+    }
+}