Fix mapping char_filter when mapping a hashtag (opensearch-project#7591)

Signed-off-by: Nathan Myles <myles.n.a@gmail.com>

Issue: opensearch-project#7308

CHANGELOG.md

@@ -93,6 +93,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 - Support OpenSSL Provider with default Netty allocator ([#5460](https://github.com/opensearch-project/OpenSearch/pull/5460))
 - Replaces ZipInputStream with ZipFile to fix Zip Slip vulnerability ([#7230](https://github.com/opensearch-project/OpenSearch/pull/7230))
 - Add missing validation/parsing of SearchBackpressureMode of SearchBackpressureSettings ([#7541](https://github.com/opensearch-project/OpenSearch/pull/7541))
+- Fix mapping char_filter when mapping a hashtag ([#7591](https://github.com/opensearch-project/OpenSearch/pull/7591))
 
 ### Security
 

modules/analysis-common/src/main/java/org/opensearch/analysis/common/MappingCharFilterFactory.java

@@ -54,7 +54,7 @@ public class MappingCharFilterFactory extends AbstractCharFilterFactory implemen
     MappingCharFilterFactory(IndexSettings indexSettings, Environment env, String name, Settings settings) {
         super(indexSettings, name);
 
-        List<MappingRule<String, String>> rules = Analysis.parseWordList(env, settings, "mappings", this::parse);
+        List<MappingRule<String, String>> rules = Analysis.parseWordList(env, settings, "mappings", this::parse, false);
         if (rules == null) {
             throw new IllegalArgumentException("mapping requires either `mappings` or `mappings_path` to be configured");
         }

modules/analysis-common/src/test/java/org/opensearch/analysis/common/MappingCharFilterFactoryTests.java

@@ -37,19 +37,19 @@ public static CharFilterFactory create(String... rules) throws IOException {
 
     public void testRulesOk() throws IOException {
         MappingCharFilterFactory mappingCharFilterFactory = (MappingCharFilterFactory) create(
-            "# This is a comment",
+            "# => _hashtag_",
             ":) => _happy_",
             ":( => _sad_"
         );
-        CharFilter inputReader = (CharFilter) mappingCharFilterFactory.create(new StringReader("I'm so :)"));
+        CharFilter inputReader = (CharFilter) mappingCharFilterFactory.create(new StringReader("I'm so :), I'm so :( #confused"));
         char[] tempBuff = new char[14];
         StringBuilder output = new StringBuilder();
         while (true) {
             int length = inputReader.read(tempBuff);
             if (length == -1) break;
             output.append(tempBuff, 0, length);
         }
-        assertEquals("I'm so _happy_", output.toString());
+        assertEquals("I'm so _happy_, I'm so _sad_ _hashtag_confused", output.toString());
     }
 
     public void testRuleError() {
@@ -64,7 +64,7 @@ public void testRuleError() {
     }
 
     public void testRulePartError() {
-        RuntimeException ex = expectThrows(RuntimeException.class, () -> create("# This is a comment", ":) => _happy_", "a:b"));
+        RuntimeException ex = expectThrows(RuntimeException.class, () -> create("# => _hashtag_", ":) => _happy_", "a:b"));
         assertEquals("Line [3]: Invalid mapping rule : [a:b]", ex.getMessage());
     }
 }

modules/analysis-common/src/yamlRestTest/resources/rest-api-spec/test/analysis-common/50_char_filters.yml

@@ -57,3 +57,21 @@
     - match:  { detail.tokenizer.tokens.0.start_offset: 0 }
     - match:  { detail.tokenizer.tokens.0.end_offset: 15 }
     - match:  { detail.tokenizer.tokens.0.position: 0 }
+---
+"mapping_with_hashtag":
+  - do:
+      indices.analyze:
+        body:
+          text: 'test #test @test'
+          tokenizer: standard
+          filter:
+            - lowercase
+          char_filter:
+            - type: mapping
+              mappings:
+                - "# => _hashsign_"
+                - "@ => _atsign_"
+  - length: { tokens: 3 }
+  - match: { tokens.0.token: test }
+  - match: { tokens.1.token: _hashsign_test }
+  - match: { tokens.2.token: _atsign_test }

server/src/main/java/org/opensearch/index/analysis/Analysis.java

@@ -222,6 +222,16 @@ public static <T> List<T> parseWordList(Environment env, Settings settings, Stri
         return parseWordList(env, settings, settingPrefix + "_path", settingPrefix, parser);
     }
 
+    public static <T> List<T> parseWordList(
+        Environment env,
+        Settings settings,
+        String settingPrefix,
+        CustomMappingRuleParser<T> parser,
+        boolean removeComments
+    ) {
+        return parseWordList(env, settings, settingPrefix + "_path", settingPrefix, parser, removeComments);
+    }
+
     /**
      * Parses a list of words from the specified settings or from a file, with the given parser.
      *
@@ -236,6 +246,17 @@ public static <T> List<T> parseWordList(
         String settingPath,
         String settingList,
         CustomMappingRuleParser<T> parser
+    ) {
+        return parseWordList(env, settings, settingPath, settingList, parser, true);
+    }
+
+    public static <T> List<T> parseWordList(
+        Environment env,
+        Settings settings,
+        String settingPath,
+        String settingList,
+        CustomMappingRuleParser<T> parser,
+        boolean removeComments
     ) {
         List<String> words = getWordList(env, settings, settingPath, settingList);
         if (words == null) {
@@ -245,7 +266,7 @@ public static <T> List<T> parseWordList(
         int lineNum = 0;
         for (String word : words) {
             lineNum++;
-            if (word.startsWith("#") == false) {
+            if (removeComments == false || word.startsWith("#") == false) {
                 try {
                     rules.add(parser.apply(word));
                 } catch (RuntimeException ex) {