Fix for converting SQL wildcard to Lucene syntax

sandbox/plugins/analytics-backend-lucene/src/main/java/org/opensearch/be/lucene/serializers/WildcardQuerySerializer.java

@@ -27,7 +27,53 @@ protected String functionName() {
 
     @Override
     protected QueryBuilder createQueryBuilder(ConversionUtils.RelevanceOperands operands) {
-        return new WildcardQueryBuilder(operands.fieldName(), operands.query());
+        String convertedPattern = convertSqlWildcardToLucene(operands.query());
+        return new WildcardQueryBuilder(operands.fieldName(), convertedPattern);
+    }
+
+    /**
+     * Converts SQL wildcard characters (% and _) to Lucene wildcard characters (* and ?).
+     * Escaped wildcards (\% and \_) are treated as literal characters.
+     * A backslash escaping another backslash (\\) produces a literal backslash.
+     */
+    private static String convertSqlWildcardToLucene(String text) {
+        final char ESCAPE = '\\';
+        StringBuilder result = new StringBuilder(text.length());
+        boolean escaped = false;
+
+        for (char c : text.toCharArray()) {
+            if (escaped) {
+                switch (c) {
+                    case '%':
+                        result.append('%');
+                        break;
+                    case '_':
+                        result.append('_');
+                        break;
+                    case ESCAPE:
+                        result.append(ESCAPE);
+                        break;
+                    default:
+                        result.append(ESCAPE);
+                        result.append(c);
+                        break;
+                }
+                escaped = false;
+            } else if (c == ESCAPE) {
+                escaped = true;
+            } else if (c == '%') {
+                result.append('*');
+            } else if (c == '_') {
+                result.append('?');
+            } else {
+                result.append(c);
+            }
+        }
+        // Trailing backslash with nothing to escape — preserve it
+        if (escaped) {
+            result.append(ESCAPE);
+        }
+        return result.toString();
     }
 
     @Override

sandbox/plugins/analytics-backend-lucene/src/test/java/org/opensearch/be/lucene/QuerySerializerRegistryTests.java

@@ -391,6 +391,157 @@ public void testWildcardQuerySerializerWithBoost() throws IOException {
         }
     }
 
+    // --- SQL-to-Lucene wildcard conversion tests ---
+
+    /**
+     * Tests that SQL '%' wildcard is converted to Lucene '*'.
+     */
+    public void testWildcardQueryConvertsPercentToStar() throws IOException {
+        DelegatedPredicateSerializer serializer = serializers.get(ScalarFunction.WILDCARD_QUERY);
+        RexCall call = buildSingleFieldRexCallWithParams("title", "test%", "WILDCARD_QUERY", Map.of());
+        List<FieldStorageInfo> fieldStorage = List.of(
+            new FieldStorageInfo("title", "text", FieldType.TEXT, List.of(), List.of("lucene"), List.of(), false)
+        );
+
+        byte[] serialized = serializer.serialize(call, fieldStorage);
+
+        try (StreamInput input = new NamedWriteableAwareStreamInput(StreamInput.wrap(serialized), WRITEABLE_REGISTRY)) {
+            WildcardQueryBuilder wildcardQb = (WildcardQueryBuilder) input.readNamedWriteable(QueryBuilder.class);
+            assertEquals("test*", wildcardQb.value());
+        }
+    }
+
+    /**
+     * Tests that SQL '_' wildcard is converted to Lucene '?'.
+     */
+    public void testWildcardQueryConvertsUnderscoreToQuestionMark() throws IOException {
+        DelegatedPredicateSerializer serializer = serializers.get(ScalarFunction.WILDCARD_QUERY);
+        RexCall call = buildSingleFieldRexCallWithParams("title", "te_t", "WILDCARD_QUERY", Map.of());
+        List<FieldStorageInfo> fieldStorage = List.of(
+            new FieldStorageInfo("title", "text", FieldType.TEXT, List.of(), List.of("lucene"), List.of(), false)
+        );
+
+        byte[] serialized = serializer.serialize(call, fieldStorage);
+
+        try (StreamInput input = new NamedWriteableAwareStreamInput(StreamInput.wrap(serialized), WRITEABLE_REGISTRY)) {
+            WildcardQueryBuilder wildcardQb = (WildcardQueryBuilder) input.readNamedWriteable(QueryBuilder.class);
+            assertEquals("te?t", wildcardQb.value());
+        }
+    }
+
+    /**
+     * Tests that escaped SQL wildcards (\% and \_) are treated as literal characters.
+     */
+    public void testWildcardQueryEscapedWildcardsRemainLiteral() throws IOException {
+        DelegatedPredicateSerializer serializer = serializers.get(ScalarFunction.WILDCARD_QUERY);
+        RexCall call = buildSingleFieldRexCallWithParams("title", "100\\%\\_done", "WILDCARD_QUERY", Map.of());
+        List<FieldStorageInfo> fieldStorage = List.of(
+            new FieldStorageInfo("title", "text", FieldType.TEXT, List.of(), List.of("lucene"), List.of(), false)
+        );
+
+        byte[] serialized = serializer.serialize(call, fieldStorage);
+
+        try (StreamInput input = new NamedWriteableAwareStreamInput(StreamInput.wrap(serialized), WRITEABLE_REGISTRY)) {
+            WildcardQueryBuilder wildcardQb = (WildcardQueryBuilder) input.readNamedWriteable(QueryBuilder.class);
+            assertEquals("100%_done", wildcardQb.value());
+        }
+    }
+
+    /**
+     * Tests mixed SQL wildcards and escaped wildcards in a single pattern.
+     */
+    public void testWildcardQueryMixedEscapedAndUnescaped() throws IOException {
+        DelegatedPredicateSerializer serializer = serializers.get(ScalarFunction.WILDCARD_QUERY);
+        RexCall call = buildSingleFieldRexCallWithParams("title", "%foo\\_bar_", "WILDCARD_QUERY", Map.of());
+        List<FieldStorageInfo> fieldStorage = List.of(
+            new FieldStorageInfo("title", "text", FieldType.TEXT, List.of(), List.of("lucene"), List.of(), false)
+        );
+
+        byte[] serialized = serializer.serialize(call, fieldStorage);
+
+        try (StreamInput input = new NamedWriteableAwareStreamInput(StreamInput.wrap(serialized), WRITEABLE_REGISTRY)) {
+            WildcardQueryBuilder wildcardQb = (WildcardQueryBuilder) input.readNamedWriteable(QueryBuilder.class);
+            assertEquals("*foo_bar?", wildcardQb.value());
+        }
+    }
+
+    /**
+     * Tests that a pattern with no SQL wildcards passes through unchanged.
+     */
+    public void testWildcardQueryNoSqlWildcardsPassesThrough() throws IOException {
+        DelegatedPredicateSerializer serializer = serializers.get(ScalarFunction.WILDCARD_QUERY);
+        RexCall call = buildSingleFieldRexCallWithParams("title", "hello*world?", "WILDCARD_QUERY", Map.of());
+        List<FieldStorageInfo> fieldStorage = List.of(
+            new FieldStorageInfo("title", "text", FieldType.TEXT, List.of(), List.of("lucene"), List.of(), false)
+        );
+
+        byte[] serialized = serializer.serialize(call, fieldStorage);
+
+        try (StreamInput input = new NamedWriteableAwareStreamInput(StreamInput.wrap(serialized), WRITEABLE_REGISTRY)) {
+            WildcardQueryBuilder wildcardQb = (WildcardQueryBuilder) input.readNamedWriteable(QueryBuilder.class);
+            assertEquals("hello*world?", wildcardQb.value());
+        }
+    }
+
+    /**
+     * Tests that an escaped backslash (\\) followed by a wildcard correctly produces
+     * a literal backslash plus the converted wildcard.
+     */
+    public void testWildcardQueryEscapedBackslashFollowedByWildcard() throws IOException {
+        DelegatedPredicateSerializer serializer = serializers.get(ScalarFunction.WILDCARD_QUERY);
+        // Java string "\\\\%" is runtime chars: \, \, %
+        // Expected: first \ escapes second \ → literal \, then % is unescaped → *
+        RexCall call = buildSingleFieldRexCallWithParams("title", "\\\\%", "WILDCARD_QUERY", Map.of());
+        List<FieldStorageInfo> fieldStorage = List.of(
+            new FieldStorageInfo("title", "text", FieldType.TEXT, List.of(), List.of("lucene"), List.of(), false)
+        );
+
+        byte[] serialized = serializer.serialize(call, fieldStorage);
+
+        try (StreamInput input = new NamedWriteableAwareStreamInput(StreamInput.wrap(serialized), WRITEABLE_REGISTRY)) {
+            WildcardQueryBuilder wildcardQb = (WildcardQueryBuilder) input.readNamedWriteable(QueryBuilder.class);
+            assertEquals("\\*", wildcardQb.value());
+        }
+    }
+
+    /**
+     * Tests that a backslash before a non-wildcard character preserves both characters.
+     */
+    public void testWildcardQueryBackslashBeforeNonWildcard() throws IOException {
+        DelegatedPredicateSerializer serializer = serializers.get(ScalarFunction.WILDCARD_QUERY);
+        // Java string "\\n" is runtime chars: \, n
+        RexCall call = buildSingleFieldRexCallWithParams("title", "test\\n", "WILDCARD_QUERY", Map.of());
+        List<FieldStorageInfo> fieldStorage = List.of(
+            new FieldStorageInfo("title", "text", FieldType.TEXT, List.of(), List.of("lucene"), List.of(), false)
+        );
+
+        byte[] serialized = serializer.serialize(call, fieldStorage);
+
+        try (StreamInput input = new NamedWriteableAwareStreamInput(StreamInput.wrap(serialized), WRITEABLE_REGISTRY)) {
+            WildcardQueryBuilder wildcardQb = (WildcardQueryBuilder) input.readNamedWriteable(QueryBuilder.class);
+            assertEquals("test\\n", wildcardQb.value());
+        }
+    }
+
+    /**
+     * Tests that a trailing backslash is preserved in the output.
+     */
+    public void testWildcardQueryTrailingBackslash() throws IOException {
+        DelegatedPredicateSerializer serializer = serializers.get(ScalarFunction.WILDCARD_QUERY);
+        // Java string "test\\" is runtime chars: t, e, s, t, \
+        RexCall call = buildSingleFieldRexCallWithParams("title", "test\\", "WILDCARD_QUERY", Map.of());
+        List<FieldStorageInfo> fieldStorage = List.of(
+            new FieldStorageInfo("title", "text", FieldType.TEXT, List.of(), List.of("lucene"), List.of(), false)
+        );
+
+        byte[] serialized = serializer.serialize(call, fieldStorage);
+
+        try (StreamInput input = new NamedWriteableAwareStreamInput(StreamInput.wrap(serialized), WRITEABLE_REGISTRY)) {
+            WildcardQueryBuilder wildcardQb = (WildcardQueryBuilder) input.readNamedWriteable(QueryBuilder.class);
+            assertEquals("test\\", wildcardQb.value());
+        }
+    }
+
     // --- QuerySerializer (no-field) tests ---
 
     /**